Network Working Group F. L. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Standards Track 21 March 2025
Expires: 22 September 2025
Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero3-36
Abstract
This document specifies an Automatic Extended Route Optimization
(AERO) service for IP internetworking over Overlay Multilink Network
(OMNI) Interfaces. AERO/OMNI uses IPv6 Neighbor Discovery (IPv6 ND)
for control plane messaging over the OMNI virtual link. Router
discovery and neighbor coordination are employed for network
admission and to manage the OMNI link forwarding and routing systems.
Secure multilink path selection, multinet traversal, mobility
management, multicast forwarding, multihop operation and route
optimization are naturally supported through dynamic neighbor cache
updates on a per flow basis. Both Provider-Aggregated (PA) and
Provider-Independent (PI) addressing services are supported. AERO is
a widely-applicable service especially well-suited for air/land/sea/
space mobility applications including aviation, intelligent
transportation systems, mobile end user devices, space exploration
and many others.
Status of This Memo
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 19
4. Automatic Extended Route Optimization (AERO) . . . . . . . . 19
4.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 19
4.2. The AERO Service over OMNI Links . . . . . . . . . . . . 20
4.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 21
4.2.2. AERO Addressing . . . . . . . . . . . . . . . . . . . 24
4.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 26
4.2.4. Segment Routing Topologies (SRTs) . . . . . . . . . . 28
4.2.5. Segment Routing For OMNI Link Selection . . . . . . . 29
4.3. OMNI Interface Characteristics . . . . . . . . . . . . . 29
4.4. OMNI Interface Initialization . . . . . . . . . . . . . . 31
4.4.1. AERO Gateway Behavior . . . . . . . . . . . . . . . . 32
4.4.2. AERO Proxy/Server and Relay Behavior . . . . . . . . 32
4.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 32
4.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 33
4.5.1. AERO/OMNI Control Plane Messages . . . . . . . . . . 36
4.5.2. OMNI Neighbor Window Synchronization . . . . . . . . 39
4.6. OMNI Interface Encapsulation and Fragmentation . . . . . 40
4.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 42
4.8. OMNI Interface Data Origin Authentication . . . . . . . . 43
4.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 43
4.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 44
4.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 46
4.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 47
4.10.3. Gateway Forwarding Algorithm . . . . . . . . . . . . 49
4.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 51
4.12. AERO Mobility Service Coordination . . . . . . . . . . . 54
4.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 54
4.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 56
4.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 57
4.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization . . . . . . . . . . . . . . . . . . . . . . 62
4.13.1. Multilink Address Resolution . . . . . . . . . . . . 64
4.13.2. Multilink Forwarding . . . . . . . . . . . . . . . . 69
4.13.3. Mobile Ad-hoc Network (MANET) Forwarding . . . . . . 80
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4.13.4. Proxy/Server-to-Proxy/Server Route Optimization . . 82
4.13.5. Gateway-to-Proxy/Server Route Optimization . . . . . 82
4.13.6. Client-to-Client Route Optimization . . . . . . . . 82
4.13.7. Intra-(M)ANET/ENET Route Optimization . . . . . . . 84
4.14. Neighbor Unreachability Detection (NUD) . . . . . . . . . 85
4.15. Mobility Management and Quality of Service (QoS) . . . . 86
4.15.1. Mobility Update Messaging . . . . . . . . . . . . . 87
4.15.2. Announcing Link-Layer Information Changes . . . . . 88
4.15.3. Bringing New Links Into Service . . . . . . . . . . 88
4.15.4. Deactivating Existing Links . . . . . . . . . . . . 88
4.15.5. Moving Between Proxy/Servers . . . . . . . . . . . . 89
4.15.6. Accommodating Path Changes . . . . . . . . . . . . . 90
4.16. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 91
4.16.1. Source-Specific Multicast (SSM) . . . . . . . . . . 92
4.16.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 93
4.16.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 94
4.17. Operation over Multiple OMNI Links . . . . . . . . . . . 94
4.18. DNS Considerations . . . . . . . . . . . . . . . . . . . 95
4.19. Transition/Coexistence Considerations . . . . . . . . . . 95
4.20. Proxy/Server-Gateway Bidirectional Forwarding
Detection . . . . . . . . . . . . . . . . . . . . . . . 96
4.21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 96
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 96
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 97
7. Security Considerations . . . . . . . . . . . . . . . . . . . 97
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 100
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 102
9.1. Normative References . . . . . . . . . . . . . . . . . . 102
9.2. Informative References . . . . . . . . . . . . . . . . . 104
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 111
A.1. Implementation Strategies for Route Optimization . . . . 111
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 112
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 112
A.4. AERO Critical Infrastructure Considerations . . . . . . . 113
A.5. AERO Server Failure Implications . . . . . . . . . . . . 113
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 114
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 116
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 119
1. Introduction
Automatic Extended Route Optimization (AERO) fulfills the
requirements of Distributed Mobility Management (DMM) [RFC7333] and
route optimization [RFC5522] for air/land/sea/space mobility
applications including aeronautical networking intelligent
transportation systems, home network users, enterprise mobile device
users, space exploration and many others. AERO is a secure
internetworking and mobility management service that employs the
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Overlay Multilink Network Interface (OMNI) [I-D.templin-6man-omni3]
with its Non-Broadcast, Multiple Access (NBMA) virtual link model.
The OMNI link is an adaptation layer virtual overlay manifested by
IPv6 encapsulation over a network-of-networks concatenation of
underlay Internetworks. Nodes on the link can exchange original IP
packets or parcels (see: [I-D.templin-6man-parcels2] and
[I-D.templin-intarea-parcels2]) as single-hop neighbors; both IP
protocol versions (IPv4 and IPv6) are supported. The OMNI Adaptation
Layer (OAL) supports multilink operation for increased reliability
and path optimization while providing fragmentation and reassembly
services to support improved performance and Maximum Transmission
Unit (MTU) diversity. This specification provides a mobility service
architecture companion to the OMNI specification.
The AERO service connects Clients as OMNI link end systems via Proxy/
Servers and Relays as intermediate systems as necessary; AERO further
employs Gateways that interconnect diverse Internetworks as OMNI link
segments through OAL forwarding at a layer below IP. Each node's
OMNI interface supports the operation of IPv6 Neighbor Discovery
(IPv6 ND) [RFC4861] as the mobility service control message protocol.
A Client's OMNI interface can be configured over multiple underlay
interfaces, and therefore appears as a single interface with multiple
link layer addresses. Each link layer address is subject to change
due to mobility and/or multilink fluctuations, and link layer address
changes are signaled by ND messaging the same as for any IPv6 link.
AERO provides a secure virtual link overlay service where mobile node
Clients use Proxy/Servers acting as proxys and/or designated routers
while correspondent nodes on foreign networks may use any Relay on
the link for efficient communications. Foreign network correspondent
nodes forward original IP packets/parcels destined to other AERO
nodes via the nearest Relay, which forwards them through the cloud.
Mobile node Clients discover shortest paths to OMNI link neighbors
through AERO route optimization. Both unicast and multicast
communications are supported.
AERO supports both Provider-Aggregated (PA) and Provider-Independent
(PI) addressing. Correspondent nodes on foreign networks configure
PA addresses from Foreign Network Prefixes (FNPs) advertised by
Relays. AERO Clients instead obtain stable PA addresses from Stable
Network Prefixes (SNPs) assigned to and managed by First Hop Segment
(FHS) Proxy/Servers. Mobile node Clients can also register PI Mobile
Network Prefixes (MNPs) with Mobility Anchor Point (MAP) Proxy/
Servers to support Internetworking for mobile routers.
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AERO Clients receive SNP (PA) addresses and optionally also MNP (PI)
prefix delegations through control message exchanges with Proxy/
Servers over their local networks. Proxy/Servers provide anchor
points for both local network PA operation and global mobility. By
linking mobile PI prefixes with stable PA addresses, the AERO service
supports the best aspects of PA/PI working together.
AERO Gateways peer with Proxy/Servers in a secured private BGP
overlay routing instance to establish a Segment Routing Topology
(SRT) virtual spanning tree over the underlay Internetworks of one or
more disjoint administrative domains concatenated as a single unified
OMNI link. Each OMNI link instance is characterized by a set of
Mobility Service Prefixes (MSPs) common to all mobile nodes. Relays
provide an optimal route from correspondent nodes on foreign links/
networks to mobile or fixed nodes on the local OMNI link. From the
perspective of underlay Internetworks, each Relay appears as the
source of a route to the MSP; hence uplink traffic to mobile nodes is
naturally routed to the nearest Relay.
AERO is compatible with OMNI links that span private-use
Internetworks and/or public Internetworks such as the global IPv4 and
IPv6 Internets. In both cases, Clients may be located behind Network
Address Translators (NATs) on the path to their associated Proxy/
Servers and/or peers. A means for robust traversal of NATs while
avoiding "triangle routing" and critical infrastructure traffic
concentration through a service known as route optimization is
therefore provided.
AERO assumes the use of PIM Sparse Mode in support of multicast
communication. In support of Source Specific Multicast (SSM) when a
Mobile Node is the source, AERO route optimization ensures that a
shortest-path multicast tree is established with provisions for
mobility and multilink operation. In all other multicast scenarios
there are no AERO dependencies.
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AERO provides a secure aeronautical internetworking service for both
manned and unmanned aircraft, where the aircraft is treated as a
mobile node (MN) that can connect airborne Internet of Things (IoT)
sub-networks. AERO is also applicable to a wide variety of other use
cases. For example, it can be used to coordinate the links of mobile
nodes (e.g., cellphones, tablets, laptop computers, etc.) that
connect into a home enterprise network via public access networks
with Virtual Private Network (VPN) or open Internetwork services
enabled according to the appropriate security model. AERO also
supports terrestrial vehicular, urban air mobility and mobile
pedestrian communication services for intelligent transportation
systems [RFC9365]. Other applicable use cases including home and
small office networks, enterprise networks and many others represent
additional large classes of potential AERO/OMNI users.
Along with OMNI, AERO provides secured optimal routing support for
the "6 M's of Modern Internetworking", including:
1. Multilink - a mobile node's ability to coordinate multiple
diverse underlay data links as a single logical unit (i.e., the
OMNI interface) to achieve the required communications
performance and reliability objectives.
2. Multinet - the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain
network segments while maintaining seamless end-to-end
communications between mobile Clients and correspondents such as
air traffic controllers, fleet administrators, other mobile
Clients, etc.
3. Mobility - a mobile node's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlay interface address change, but without
disruptions to ongoing communication sessions with peers over the
OMNI link.
4. Multicast - the ability to send a single network transmission
that reaches multiple nodes belonging to the same interest group,
but without disturbing other nodes not subscribed to the interest
group.
5. Multihop - a mobile Client peer-to-peer relaying capability
useful when multiple forwarding hops between peers may be
necessary to reach a target peer or an infrastructure access
point connection to the OMNI link.
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6. (Performance) Maximization - the ability to exchange large
packets/parcels between peers without loss due to a link size
restriction, and to adaptively adjust packet/parcel sizes to
maintain the best performance profile for each independent
traffic flow.
The following numbered sections present the AERO specification. The
appendices at the end of the document are non-normative.
2. Terminology
The terminology in the normative references applies; especially, the
OMNI specification terminology [I-D.templin-6man-omni3] and the IPv6
Neighbor Discovery (IPv6 ND) [RFC4861] node variables, protocol
constants and message types (including Router Solicitation (RS),
Router Advertisement (RS), Neighbor Solicitation (NS), Neighbor
Advertisement (NA), unsolicited NA (uNA) and Redirect) are cited
extensively throughout. AERO further introduces new "pseudo" IPv6 ND
message types Multilink Initiate (MI), Multilink Respond (MR) and
Multilink Control (NC) with formats identical to the standard RS
message but with different Code values. These messages are used to
control adaptation layer functions only and are never exposed to the
network layer.
Throughout the document, the simple terms "(Proxy/)Client", "Proxy/
Server", "Gateway" and "Relay" refer to "AERO/OMNI Client", "AERO/
OMNI Proxy/Server", "AERO/OMNI Gateway" and "AERO/OMNI Relay",
respectively. Capitalization is used to distinguish these terms from
other common Internetworking uses in which they appear without
capitalization, and implies that the node in question both configures
an OMNI interface and engages the OMNI Adaptation Layer (OAL).
The terms "All-Routers multicast", "All-Nodes multicast", "Solicited-
Node multicast" and "Subnet-Router anycast" are defined in [RFC4291].
The term "IP" refers generically to either Internet Protocol version
(IPv4 [RFC0791] or IPv6 [RFC8200]) for specification elements that
apply equally to both.
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The terms "application layer (L5 and higher)", "transport layer
(L4)", "network layer (L3)", "(data) link layer (L2)" and "physical
layer (L1)" are used consistently with common Internetworking
terminology, with the understanding that reliable delivery protocol
users of UDP are considered as transport layer elements. The OMNI
specification further defines an "adaptation layer" positioned below
the network layer but above the link layer, which may include
physical links and Internet- or higher-layer tunnels. A (network)
interface is a node's attachment to a link (via L2), and an OMNI
interface is therefore a node's attachment to an OMNI link (via the
adaptation layer).
The terms "IP jumbogram", "advanced jumbo (AJ)" and "IP parcel" refer
to special packet formats that enable a new link model for the
Internet as discussed in [I-D.templin-6man-parcels2]
[I-D.templin-intarea-parcels2].
The following terms are defined within the scope of this document:
IPv6 Neighbor Discovery (IPv6 ND)
a control message service for coordinating neighbor relationships
between nodes connected to a common link. AERO uses the IPv6 ND
messaging service specified in [RFC4861] in conjunction with the
OMNI extensions specified in [I-D.templin-6man-omni3].
IPv6 Prefix Delegation (IPv6 PD)
a networking service for delegating IPv6 prefixes to nodes on the
link. AERO nodes apply the IPv6 PD service provided by DHCPv6
[I-D.ietf-dhc-rfc8415bis] in conjunction with OMNI interface IPv6
ND.
GUA, ULA, LLA, MLA
A Globally-Unique (GUA), Unique-Local (ULA) or Link-Local (LLA)
Address per the IPv6 addressing architecture [RFC4193] [RFC4291],
or a Multilink-Local Address (MLA) per [I-D.templin-6man-mla].
IPv4 prefixes other than those reserved for special purposes
[RFC6890] are also considered as GUA prefixes.
L3
The Network layer in the OSI network model. Also known as "layer
3", "IP layer", etc.
L2
The Data Link layer in the OSI network model. Also known as
"layer 2", "link layer", "sub-IP layer", etc.
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Adaptation Layer
An encapsulation mid-layer that adapts L3 to a diverse collection
of L2 underlay interfaces and their encapsulations. (No layer
number is assigned, since numbering was an artifact of the legacy
reference model that need not carry forward in the modern
architecture.) The adaptation layer sees the network layer as
"L3" and sees all link layer encapsulations as "L2
encapsulations", which may include UDP, IP and true link layer
(e.g., Ethernet, etc.) headers.
Access Network (ANET)
a connected network region (e.g., an aviation radio access
network, corporate enterprise network, satellite service provider
network, cellular operator network, residential WiFi network,
etc.) that connects Clients to the Mobility Service over the OMNI
link. Physical and/or data link level security is assumed and
sometimes referred to as "protected spectrum" for wireless
domains. Private enterprise networks and ground domain aviation
service networks may provide multiple secured IP hops between the
Client's point of connection and the nearest Proxy/Server.
Mobile Ad-hoc NETwork (MANET)
a connected ANET region for which links often have undetermined
connectivity properties, lower layer security services cannot
always be assumed and multihop forwarding between Clients acting
as MANET routers may be necessary.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between (M)ANETs and AERO/
OMNI nodes that coordinate with the Mobility Service over
unprotected media. No physical and/or data link level security is
assumed, therefore security must be applied by the network and/or
higher layers. The global public Internet itself is an example.
End-user Network (ENET)
a simple or complex "downstream" network tethered to a Client as a
single logical unit that travels together. The ENET could be as
simple as a single link connecting a single end system, or as
complex as a large network with many links, routers, bridges and
end user devices. The ENET provides an "upstream" link for
arbitrarily many low-, medium- or high-end devices dependent on
the Client for their upstream connectivity, i.e., as Internet of
Things (IoT) entities. ENETs can also support a recursively-
descending chain of additional Clients such that the ENET of an
upstream Client is seen as the ANET of a downstream Client.
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*NET
a "wildcard" term used when a given specification applies equally
to all MANET/ANET/INET cases. From the Client's perspective, *NET
interfaces are "upstream" interfaces that connect the Client to
the Mobility Service, while ENET interfaces are "downstream"
interfaces that the Client uses to connect downstream *NETs which
may connect other Clients. Local communications between
correspondents within the same *NET can often be conducted based
on IPv6 ULAs [RFC4193] or MLAs [I-D.templin-6man-mla].
underlay network/interface
a *NET or ENET network/interface over which an OMNI interface is
configured. The OMNI interface is seen as a network layer (L3)
interface by the IP layer, and the OMNI adaptation layer sees the
underlay interface as a data link layer (L2) interface. The
underlay interface either connects directly to the physical or
virtual communications media or coordinates with another node that
hosts the media.
MANET Interface
a node's underlay interface to a local network with indeterminant
neighborhood properties over which multihop relaying may be
necessary. All MANET interfaces used by AERO/OMNI are IPv6
interfaces and therefore must configure a Maximum Transmission
Unit (MTU) no smaller than the IPv6 minimum MTU (1280 octets) even
if lower-layer fragmentation is needed.
OMNI link
the same as defined in [I-D.templin-6man-omni3]. The OMNI link
employs IPv6 encapsulation to traverse intermediate systems in a
spanning tree over underlay network segments the same as a bridged
campus LAN. AERO nodes on the OMNI link appear as single-hop
neighbors at the network layer even though they may be separated
by many underlay network hops; AERO nodes can employ Segment
Routing [RFC8402] to navigate between different OMNI links, and/or
to cause packets/parcels to visit selected waypoints within the
same OMNI link.
OMNI link segment
a Proxy/Server and all of its constituent Clients within any
attached *NETs is considered as a leaf OMNI link segment, with
each leaf interconnected via links and "bridge" nodes in
intermediate OMNI link segments. When the *NETs of multiple leaf
segments overlap (e.g., due to network mobility), they can combine
to form larger *NETs with no changes to Client-to-Proxy/Server
relationships. The OMNI link consists of the concatenation of all
OMNI link leaf and intermediate segments as a loop-free spanning
tree.
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OMNI interface
a node's virtual Ethernet (veth) interface to an OMNI link, and
configured over one or more underlay interfaces. If there are
multiple OMNI links in an OMNI domain, a separate OMNI interface
is configured for each link. The OMNI interface configures a
Maximum Transmission Unit (MTU) and an Effective MTU to Receive
(EMTU_R) the same as any interface. The OMNI interface assigns an
LLA the same as for any IPv6 interface and assigns an MLA for
adaptation layer addressing over its underlay networks. The OMNI
interface further assigns any unicast or anycast ULA/GUA addresses
acquired through address autoconfiguration. Since OMNI interface
addresses are managed for uniqueness, OMNI interfaces do not
require Duplicate Address Detection (DAD) and therefore set the
administrative variable 'DupAddrDetectTransmits' to zero
[RFC4862].
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets/parcels admitted into the interface in an IPv6 header and/
or subjects them to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for spanning
multiple segments of an extended OMNI link.
OMNI Option
a pseudo IPv6 ND option providing multilink parameters for the
OMNI interface. The OMNI option is appended to the end of an IPv6
ND message during OAL encapsulation such that it appears
immediately following the final message option.
(network) partition
frequently, underlay networks such as large corporate enterprise
networks are sub-divided internally into separate isolated
partitions (a technique also known as "network segmentation").
Each partition is fully connected internally but disconnected from
other partitions, and there is no requirement that separate
partitions maintain consistent Internet Protocol and/or addressing
plans. (Each partition is seen as a separate OMNI link
(multi-)segment as discussed throughout this document.)
(OMNI) L2 encapsulation
the OMNI protocol encapsulation of OAL packets/fragments in an
outer header or headers to form carrier packets that can be routed
within the scope of the local *NET or ENET underlay network
partition. Common L2 encapsulation combinations include UDP/IP/
Ethernet, etc. using a port/protocol/type number for OMNI.
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L2 address (L2ADDR)
an address that appears in the L2 encapsulation for an underlay
interface and also in IPv6 ND message OMNI options. L2ADDR can be
either an IP address for IP encapsulations or an IEEE EUI address
[EUI] for direct data link encapsulation. (When UDP/IP
encapsulation is used, the UDP port number is regarded as an
extension of the IP L2ADDR.)
original IP packet/parcel
a whole IP packet/parcel or fragment admitted into the OMNI
interface by the network layer prior to OAL encapsulation/
fragmentation, or an IP packet/parcel delivered to the network
layer by the OMNI interface following OAL reassembly/
decapsulation.
OAL packet
an original IP packet/parcel encapsulated in an OAL IPv6 header
with an IPv6 Extended Fragment Header extension that includes an
8-octet (64-bit) OAL Identification value. Each OAL packet is
then subject to OAL fragmentation and reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to L2
encapsulation/fragmentation, or following L2 reassembly/
decapsulation but prior to OAL reassembly.
(OAL) atomic fragment
an OAL packet that can be forwarded without fragmentation, but
still includes an IPv6 Extended Fragment Header with an 8-octet
(64-bit) OAL Identification value and with Index and More
Fragments both set to 0. (Note that control message atomic
fragments also omit the Extended Fragment Header over secured
spanning tree links.)
(L2) carrier packet
an encapsulated OAL packet/fragment following L2 encapsulation or
prior to L2 decapsulation. OAL sources and destinations exchange
carrier packets over underlay interfaces, and may be separated by
one or more OAL intermediate systems. OAL intermediate systems
re-encapsulate OAL packets/fragments during forwarding by removing
the L2 headers of carrier packets from a previous hop underlay
network and replacing them with new L2 headers for the next hop
underlay network. Carrier packets may themselves be subject to
fragmentation and reassembly in L2 underlay networks at a layer
below the OAL. Carrier packets sent over unsecured paths use OMNI
protocol L2 encapsulations, while those sent over the secured
paths use L2 security encapsulations such as IPsec [RFC4301], etc.
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OAL source
an OMNI interface acts as an OAL source when it encapsulates
original IP packets/parcels to form OAL packets, then performs OAL
fragmentation and L2 encapsulation to create carrier packets.
Every OAL source is also an OAL end system.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly/decapsulation to
restore the original IP packet/parcel. Every OAL destination is
also an OAL end system.
OAL intermediate system
an OMNI interface acts as an OAL intermediate system when it
reassembles/decapsulates carrier packets received from a first
segment to obtain the original OAL packet/fragment, then re-
encapsulates in new L2 headers appropriate for the next segment
and sends these new carrier packets into the next segment (while
re-fragmenting first, if necessary). OAL intermediate systems
decrement the Hop Limit in OAL packets/fragments during
forwarding, and discard the OAL packet/fragment if the Hop Limit
reaches 0. OAL intermediate systems do not decrement the TTL/Hop
Limit of the original IP packet/parcel, which can only be updated
by the network and higher layers. OAL intermediate systems along
the path not explicitly addressed by the OAL IPv6 Destination
(e.g., MANET routers, AERO Gateways, etc.) are regarded as
"transit" intermediate systems.
Mobility Service Prefix (MSP)
an aggregated IP GUA prefix (e.g., 2001:db8::/32,
2002:192.0.2.0::/40, etc.) assigned to the OMNI link and from
which more-specific Mobile and Stable Network Prefixes (MNPs/SNPs)
are delegated, where IPv4 MSPs are represented as "6to4 prefixes"
per [RFC3056]. OMNI link administrators typically obtain MSPs
from an Internet address registry, however private-use prefixes
can alternatively be used subject to certain limitations (see:
[I-D.templin-6man-omni3]). OMNI links that connect to the global
Internet advertise their MSPs to interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP GUA prefix derived from an MSP (e.g.,
2001:db8:1000:2000::/56, 2002:192.0.2.8::/48, etc.) and delegated
to an AERO Client.
Stable Network Prefix (SNP)
a global and unique-local IP prefix pair assigned to one or more
Proxy/Servers that connect local *NET Client groups to the rest of
the OMNI link. Clients request address delegations from the SNP
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that can be used to support PA communications. Clients
communicate internally within (M)ANETs and INET groups using IPv6
ULAs [RFC4193] assigned in 1x1 correspondence to SNP GUAs
[RFC4291] made visible to external peers through IP network
address/prefix translation [RFC6145][RFC6146][RFC6147] [RFC6296].
Foreign Network Prefix (FNP)
a global IP prefix not covered by a MSP and assigned to a link or
network outside of the AERO/OMNI domain. Relays advertise any of
their associated FNPs into the AERO/OMNI routing system and
forward packets between MNP/SNP mobile or fixed nodes on the OMNI
link and FNP correspondent nodes on other links.
Subnet Router Anycast (SRA) Address
An IPv6 address taken from an FNP/MNP/SNP in which the remainder
of the address beyond the final bit of the prefix is set to the
value "all-zeros". For example, the SRA for 2001:db8:1::/48 is
simply 2001:db8:1:: (i.e., with the 80 least significant bits set
to 0). For IPv4, the IPv6 SRA corresponding to the IPv4 prefix
192.0.2.0/24 is 2002:192.0.2.0::/40 per [RFC3056].
Interface Identifier (IID)
the least significant 64 bits of an IPv6 address, as specified in
the IPv6 addressing architecture [RFC4291].
Provider-Aggregated (PA) Address
a ULA/GUA address pair delegated to a Client from an FHS Proxy/
Server SNP is considered Provider-Aggregated (PA) or "Proxy/
Server-Aggregated". The Client either assigns the GUA PA address
to its own OMNI interface or allows the FHS Proxy/Server to supply
the address via Network Prefix Translation for IPv6 (NPTv6)
[RFC6296].
Provider-Independent (PI) Address
a GUA allocated from an MNP delegated to a Client via a MAP Proxy/
Server is considered Provider-Independent (PI) or "Proxy/Server-
Independent". The Client assigns PI addresses to (downstream)
ENET interfaces and can sub-delegate the MNP to downstream ENET
nodes.
AERO node
a node that is connected to an OMNI link and participates in the
AERO internetworking and mobility service.
(AERO) Client
an AERO node that configures an OMNI interface over one or more
underlay interfaces and requests SNP address and/or MNP prefix
delegations from AERO Proxy/Servers. The Client assigns a variety
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of IPv6 address types to the OMNI interface for use in IPv6 ND
exchanges with other AERO nodes and forwards original IP packets/
parcels to correspondents according to OMNI interface neighbor
cache state. The Client coordinates with Proxy/Servers and/or
other Clients over upstream ANET/INET interfaces and may also
provide Proxy services for other Clients over downstream ENET
interfaces.
(AERO) Proxy/Server
an AERO node that provides a proxying service between AERO Clients
and external peers on its Client-facing (M)ANET interfaces (i.e.,
in the same fashion as for an enterprise network proxy) as well as
designated router services for coordination with correspondents on
its INET-facing interfaces. (Proxy/Servers in the open INET
instead configure only a single INET interface and no (M)ANET
interfaces.) The Proxy/Server configures an OMNI interface and
maintains BGP peerings with Gateways to provide a local anchor
point for its stable and/or mobile Clients. All Proxy/Servers
configure a Stable Network Prefix (SNP) and manage 1x1 mappings of
internal ULAs and external GUAs according to Network Prefix
Translation for IPv6 (NPTv6) [RFC6296].
(AERO) Relay
an AERO Proxy/Server that provides forwarding services between
nodes reached via the OMNI link and correspondents on foreign
links/networks. AERO Relays maintain BGP peerings with Gateways
the same as Proxy/Servers. Relays also run a dynamic routing
protocol to discover any Foreign Network Prefix (FNP) routes in
service on other links/networks, advertise OMNI link MSP(s) to
other links/networks, and redistribute FNPs discovered on other
links/networks into the OMNI link BGP routing system. (Relays
that connect to major Internetworks such as the global IPv6 or
IPv4 Internets can also be configured to advertise "default"
routes into the OMNI link BGP routing system.)
(AERO) Gateway
a BGP hub autonomous system node that also provides OAL forwarding
services for nodes on an OMNI link. Gateways forward OAL packets/
fragments between OMNI link segments as OAL intermediate systems
while decrementing the OAL IPv6 header Hop Limit but without
decrementing the network layer IP TTL/Hop Limit. Gateways peer
with Proxy/Servers and other Gateways to form an IPv6-based OAL
spanning tree over all OMNI link segments and to discover the set
of all FNP/MNP/SNP prefixes in service. Gateways process OAL
packets/fragments received over the secured spanning tree that are
addressed to themselves, while forwarding all other OAL packets/
fragments to the next hop also via the secured spanning tree.
Gateways forward OAL packets/fragments received over the unsecured
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spanning tree to the next hop either via the unsecured spanning
tree or via direct encapsulation if the next hop is on the same
OMNI link segment. It is important to note that all Gateways are
also Proxy/Servers, but only those Proxy/Servers configured as
intermediate nodes in the spanning tree are considered Gateways.
First-Hop Segment (FHS) Client
a Client that initiates communications with a target peer by
sending control messages to establish reverse-path multilink
forwarding state in OMNI link intermediate systems on the path to
the target. Note that in some arrangements the Client's (FHS)
Proxy/Server (and not the Client itself) initiates the exchange.
Last-Hop Segment (LHS) Client
a Client that responds to a communications request from a source
peer's initiation by returning a response message to establish
forward-path multilink forwarding state in OMNI link intermediate
systems on the path to the source. Note that in some arrangements
the Client's (LHS) Proxy/Server (and not the Client itself)
returns the response.
First-Hop Segment (FHS) Proxy/Server
a Proxy/Server for an FHS Client's underlay interface that
forwards the Client's OAL packets into the segment routing
topology. FHS Proxy/Servers also act as intermediate forwarding
systems to facilitate RS/RA exchanges between a Client and its MAP
Proxy/Server.
Last-Hop Segment (LHS) Proxy/Server
a Proxy/Server for an underlay interface of an LHS Client that
forwards OAL packets received from the segment routing topology to
the Client over that interface.
Mobility Anchor Point (MAP) Proxy/Server
a Proxy/Server selected by a Client that injects the Client's MNP
into the BGP routing system and provides both forwarding and
mobility services for any *NET underlay interfaces that register
the MNP. Clients often select the first FHS Proxy/Server they
coordinate with to serve in the MAP role as all FHS Proxy/Servers
are equally capable candidates to serve as a MAP. The Client can
instead select any available Proxy/Server for the OMNI link as
there is no requirement that the MAP must also be one of the
Client's FHS Proxy/Servers. This flexible arrangement supports a
fully distributed mobility management service.
Segment Routing Topology (SRT)
a Multinet OMNI link forwarding region between FHS and LHS Proxy/
Servers. FHS/LHS Proxy/Servers and SRT Gateways span the OMNI
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link on behalf of communicating peer nodes. The SRT maintains a
spanning tree established through BGP peerings between Gateways
and Proxy/Servers. Each SRT leaf segment includes Gateways in a
"hub" and Proxy/Servers in "spokes", while adjacent segments are
interconnected by Gateway-Gateway peerings. The BGP peerings are
configured over both secured and unsecured underlay network paths
such that a secured spanning tree is available for critical
control messages while other messages can use the unsecured
spanning tree.
Mobile Node (MN)
an AERO Client and all of its downstream-attached networks that
move together as a single unit, i.e., an end system and its
connected IoT sub-networks.
Mobile Router (MR)
a MN's on-board router that forwards original IP packets/parcels
between any downstream-attached networks and the OMNI link. The
MR is the MN entity that hosts the AERO Client.
Address Resolution Source (ARS)
the node nearest the original source that initiates OMNI link
address resolution. The ARS may be a Proxy/Server or Relay for
the source, or may be the source Client itself. The ARS is often
(but not always) also the same node that becomes the FHS source
during route optimization.
Address Resolution Target (ART)
the node toward which address resolution is directed. The ART may
be a Relay or the target Client itself. The ART is often (but not
always) also the same node that becomes the LHS target during
route optimization.
Address Resolution Responder (ARR)
the node that responds to address resolution requests on behalf of
the ART. The ARR may be a Relay, the ART itself, or the ART's
current MAP Proxy/Server. Note that a MAP Proxy/Server can assume
the ARR role even if it is located on a different SRT segment than
the ART. The MAP Proxy/Server assumes the ARR role only when it
receives an RS message from the ART with the 'ARR' flag set (see:
[I-D.templin-6man-omni3]).
Potential Router List (PRL)
a geographically and/or topologically referenced list of addresses
of all Proxy/Servers within the same OMNI link. Each OMNI link
has its own PRL.
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Distributed Mobility Management (DMM)
a BGP-based overlay routing service coordinated by Proxy/Servers
and Gateways that tracks all Proxy/Server-to-Client associations.
Mobility Service (MS)
the collective set of all Proxy/Servers, Gateways and Relays that
provide the AERO Service to Clients.
AERO Forwarding Information Base (AFIB)
A forwarding table on each OAL source, destination and
intermediate system that includes AERO Forwarding Vectors (AFV)
with both multilink forwarding instructions and context for
reconstructing compressed headers for specific communicating peer
underlay interface pairs. The AFIB also supports route
optimization where one or more OAL intermediate systems in the
path can be "skipped" to reduce path stretch and decrease load on
critical infrastructure elements.
AERO Forwarding Vector (AFV)
An AFIB entry that includes soft state for each underlay interface
pairwise communication session between peer neighbors. AFVs are
identified by an AFV Index (AFVI) paired with the previous hop L2
address, with the pair established based on an IPv6 ND message
exchanges. The AFV also caches underlay interface Identification
sequence number parameters to support carrier packet filtering.
AERO Forwarding Vector Index (AFVI)
A 2-octet or 4-octet integer value supplied by a previous hop OAL
node when it requests a next hop OAL node to create an AFV. (The
AFVI is always processed as a 4-octet value, but compressed
headers may omit the 2 most significant octets when they encode
the value 0.) The next hop OAL node caches the AFVI and L2
address supplied by the previous hop as header compression/
decompression state for future OAL packets with compressed
headers. The previous hop OAL node must ensure that the AFVI
values it assigns to the next hop via a specific underlay
interface are distinct and reused only after their useful
lifetimes expire. The special value 0 means that no AFVI is
asserted.
flow
A sequence of packets sent from a particular source to a
particular unicast, anycast, or multicast destination that a node
desires to label as a flow. The 3-tuple of the Flow Label, Source
Address and Destination Address fields enable efficient IPv6 flow
classification. The IPv6 Flow Label Specification is observed per
[RFC6437] [RFC6438].
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3. Requirements
OMNI interfaces limit the size of their IPv6 ND control plane
messages (plus any original IP packet/parcel attachments) to the
minimum IPv6 link MTU minus overhead for adaptation and link layer
encapsulation. If there are sufficient OMNI parameters and/or IP
packet/parcel attachments that would exceed this size, the OMNI
interface forwards the information as multiple smaller IPv6 ND
messages and the recipient accepts the union of all information
received. This allows the messages to travel without loss due to a
size restriction over secured control plane paths that include IPsec
tunnels [RFC4301], secured direct point-to-point links and/or
unsecured paths that require an authentication signature.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
4. Automatic Extended Route Optimization (AERO)
The following sections specify the operation of IP over OMNI links
using the AERO service:
4.1. AERO Node Types
AERO Clients can be deployed as fixed infrastructure nodes close to
end systems, or as Mobile Nodes (MNs) that can change their network
attachment points dynamically. AERO Clients configure OMNI
interfaces over underlay interfaces with addresses that may change
due to mobility. AERO Clients receive PA SNP addresses from their
Proxy/Servers. AERO Clients that obtain PI MNPs register them with
the AERO service, and distribute the MNPs to ENETs (which may connect
other Clients). AERO Clients provide Proxy services for Clients on
downstream-attached ENETs.
AERO Gateways, Proxy/Servers and Relays are critical infrastructure
elements in fixed (i.e., non-mobile) *NET boundary (or standalone
INET) deployments and hence have permanent and unchanging INET
addresses. Together, they provide access to the AERO service OMNI
link virtual overlay for connecting AERO Clients. AERO Gateways
(together with Proxy/Servers and Relays) provide the secured backbone
supporting infrastructure for a Segment Routing Topology (SRT)
spanning tree for the OMNI link.
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AERO Gateways are Proxy/Servers deployed as OMNI link intermediate
systems that forward packets both within the same SRT segment and
between disjoint SRT segments based on an IPv6 encapsulation mid-
layer known as the OMNI Adaptation Layer (OAL). The OMNI interface
and OAL provide an adaptation layer forwarding service that the
network layer perceives as L2 bridging, since the inner IP TTL/Hop
Limit is not decremented. Each Gateway peers with Proxy/Servers,
Relays and other Gateways in a dynamic routing protocol instance as a
Distributed Mobility Management (DMM) service for the list of active
MNPs (see: Section 4.2.3). Gateways assign one or more Mobility
Service Prefixes (MSPs) to the OMNI link and configure secured
tunnels with Proxy/Servers, Relays and other Gateways; they further
maintain forwarding table entries for each FNP/MNP/SNP prefix in
service on the OMNI link.
AERO Proxy/Servers distributed across one or more SRT segments
provide default forwarding and mobility/multilink services for AERO
Client mobile nodes. Each Proxy/Server acts as either an OMNI link
intermediate system or end system according to the service model
selected by the Client. Proxy/Servers also peer with Gateways in an
adaptation layer dynamic routing protocol instance to advertise its
list of associated MNPs (see Section 4.2.3). MAP Proxy/Servers
provide prefix delegation services and track the mobility/multilink
profiles of each of their associated Clients, where each delegated
prefix becomes an MNP taken from an MSP. Proxy/Servers at *NET
boundaries provide a primary forwarding service for (M)ANET Client
communications with peers in external INETs. Proxy/Servers in open
INETs provide an authentication service for IPv6 ND messages but
should be used only as a last resort data plane forwarding service
when a Client cannot forward directly to an INET peer. Source
Clients securely coordinate with target Clients by sending control
messages via a First-Hop Segment (FHS) Proxy/Server which forwards
them over the SRT spanning tree to a Last-Hop Segment (LHS) Proxy/
Server which finally forwards them to the target.
AERO Relays are Proxy/Servers that provide forwarding services to
exchange original IP packets/parcels between the OMNI link and fixed
or mobile nodes on other links/networks. Relays run a dynamic
routing protocol to discover any FNP prefixes in service on foreign
links/networks, and Relays that connect to larger Internetworks (such
as the Internet) may originate default routes. The Relay
redistributes OMNI link MSP(s) into other links/networks, and
redistributes FNPs via OMNI link Gateway BGP peerings.
4.2. The AERO Service over OMNI Links
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4.2.1. AERO/OMNI Reference Model
Figure 1 presents the basic OMNI link reference model:
+-----------------+
| AERO Gateway G1 |
| Nbr: S1, S2, P1 |
|(X1->S1; X2->S2) |
| MSP M1 |
+--------+--------+
+--------------+ | +--------------+
| AERO P/S S1 | | | AERO P/S S2 |
| Nbr: C1, G1 | | | Nbr: C2, G1 |
| default->G1 | | | default->G1 |
| X1->C1 | | | X2->C2 |
+-------+------+ | +------+-------+
| OMNI link | |
X===+===+==================+===================+===+===X
| |
+-----+--------+ +--------+-----+
|AERO Client C1| |AERO Client C2|
| Nbr: S1 | | Nbr: S2 |
| default->S1 | | default->S2 |
| MNP X1 | | MNP X2 |
+------+-------+ +-----+--------+
| |
.-. .-.
,-( _)-. +-------+ +-------+ ,-( _)-.
.-(_ IP )-. |IP end | |IP end | .-(_ IP )-.
(__ ENET )--|system | |system |--(__ ENET )
`-(______)-' +-------+ +-------+ `-(______)-'
Figure 1: AERO/OMNI Reference Model
In this model:
* the OMNI link is an overlay network service configured over one or
more underlay SRT segments which may be managed by diverse
administrative domains using incompatible protocols and/or
addressing plans.
* AERO Gateway G1 aggregates Mobility Service Prefix (MSP) M1,
discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP
via BGP peerings over secured tunnels to other Gateways in the SRT
(not shown). Together, the set of all Gateways provide the
backbone for an SRT spanning tree for the OMNI link.
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* AERO Proxy/Servers S1 and S2 configure secured tunnels with
Gateway G1 and also provide mobility, multilink, multicast and
default router services for the MNPs of their associated Clients
C1 and C2. (Proxy/Servers that act as Relays can also advertise
FNP routes for non-mobile correspondent nodes the same as for MNP
Clients.)
* AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2,
respectively. They receive MNP delegations X1 and X2, and also
act as default routers for their associated physical or internal
virtual ENETs. (While not shown, AERO Clients can also be
recursively nested in an arbitrarily-deep chain of (Proxy/)Clients
between a Proxy/Server and the ultimate IP end systems.)
* IP end systems attach to the ENETs served by Clients C1 and C2,
respectively. (Although not depicted here, there may be multiple
Proxy/Client intermediate systems between Clients C1 and C2 and
the ultimate IP end systems.)
An OMNI link configured over a single underlay network appears as a
single unified link with a consistent addressing plan; all nodes on
the link can exchange carrier packets via simple L2 encapsulation
(i.e., following any necessary NAT traversal) since the underlay is
connected. In common practice, however, OMNI links are often
configured over an SRT spanning tree that bridges multiple distinct
underlay network segments managed under different administrative
authorities (e.g., as for worldwide aviation service providers such
as ARINC, SITA, Inmarsat, etc.). Individual underlay networks may
also be partitioned internally, in which case each internal partition
appears as a separate segment.
The addressing plan of each SRT segment is consistent internally but
will often bear no relation to the addressing plans of other
segments. Each segment is also likely to be separated from others by
network security devices (e.g., firewalls, proxys, packet filtering
gateways, etc.), and disjoint segments often have no common physical
link connections. Therefore, nodes can only be assured of exchanging
carrier packets directly with correspondents in the same segment, and
not with those in other segments. The only means for joining the
segments therefore is through inter-domain peerings between AERO
Gateways.
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The OMNI link spans multiple SRT segments using the OAL to provide
the network layer with a virtual abstraction similar to a bridged
campus LAN. The OAL is an OMNI interface sublayer that inserts a
mid-layer IPv6 encapsulation header for inter-segment forwarding
(i.e., bridging) without decrementing the network layer TTL/Hop Limit
of the original IP packet/parcel. An example OMNI link SRT is shown
in Figure 2:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. .
. .
. .-(::::::::) .-(::::::::) .-(::::::::) .
. .-(::::::::::::)-. +-+ .-(::::::::::::)-. +-+ .-(::::::::::::)-. .
. (:::: FHS :::)--|G|--(::: Intermediate ::)--|G|--(:::: LHS :::) .
. `-(::::::::::::)-' +-+ `-(::Segments::)-' +-+ `-(::::::::::::)-' .
. `-(::::::)-' `-(::::::)-' `-(::::::)-' .
. | | .
. +---+ +---+ .
. |P/S| |P/S| .
. +---+ +---+ .
. | | .
. .-(::::::::) .-(::::::::) .
. .-(: First Hop :)-. +-------+ +-------+ .-(: Last Hop :)-. .
. (:::: Access ::::)--| Source| | Target|--(:::: Access ::::) .
. `-(:: Network ::)-' | Client| | Client| (:: Network ::)-' .
. `-(::::::)-' +-------+ +-------+ `-(::::::)-' .
. .
. .
. <-- Segment Routing Topology (SRT) Spanned by OMNI Link --> .
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2: OMNI Link Segment Routing Topology (SRT)
In the Segment Routing Topology, a source Client connects via a first
hop access network served by a First Hop Segment (FHS) Proxy/Server.
The FHS Proxy/Server then forwards to an FHS Gateway which connects
to an arbitrarily complex set of Intermediate Segments. Adjacent
intermediate Segments are joined by intermediate Gateways (not shown)
that serve as adaptation layer IPv6 routers, with the final segment
connected by a Last Hop Segment (LHS) Gateway. The LHS Gateway then
forwards to an LHS Proxy/Server which in turn connects to the last
hop access network where the target Client resides.
Gateway, Proxy/Server and Relay OMNI interfaces are configured over
both secured tunnels and open INET underlay interfaces within their
respective SRT segments. Within each segment, Gateways configure
"hub-and-spokes" BGP peerings with Proxy/Servers and Relays as
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"spokes". Adjacent SRT segments are joined by Gateway-to-Gateway
peerings to collectively form a spanning tree over the entire SRT.
The "secured spanning tree" supports authentication and integrity for
critical control plane messages (and any trailing data plane message
extensions). The "unsecured spanning tree" conveys ordinary carrier
packets without security codes and that must be examined by
destinations according to data origin authentication procedures.
AERO nodes can employ route optimization to cause carrier packets to
take more direct paths between OMNI link neighbors without having to
follow strict spanning tree paths.
The network of networks concept emerged from the earliest days of
Internetworking beginning in the 1960's [KAHN]. The concept has
carried forward to the present day where the Internet has become
successful beyond measure. The AERO Multinet service concatenates
SRT segments through Gateway-to-Gateway peerings as suggested in the
"Catenet Model for Internetworking (IEN48)" [CERF]. Catenet
suggested a concatenation of independent and diverse Internetwork
"segments" to form a much larger network supporting end-to-end
services.
The Catenet vision originally articulated in the 1970's faded into
obscurity as the Internet evolved in the decades that followed, and
the adaptation layer was omitted from the architecture. As a result,
the Internet has evolved to become a monolithic public routing and
addressing service interconnecting private domains leading to the
rise of the middle and a diminished role for end-to-end [RFC3724].
The adaptation layer manifested by AERO and OMNI now promises to
restore the best aspects of end-to-end envisioned by Catenet through
incremental deployment in the modern Internet.
4.2.2. AERO Addressing
AERO nodes on OMNI links use the Link-Local Address (LLA) prefix
fe80::/64 to assign an LLA with randomized EUI-64 interface
identifier to the OMNI interface per [RFC4291]. AERO Proxy/Servers
use their LLAs as the Source Address for Router Advertisement and
Redirect messages as required by [RFC4861], while AERO Clients use
their LLAs as Source/Destination Address for NS/NA/uNA messages. The
OMNI interface maintains an internal adaptation layer mapping cache
that translates the LLAs seen by the network layer into Multilink
Local Addresses (MLAs) included in actual IPv6 ND message exchanges
with neighbors. (See: [I-D.templin-6man-omni3] for a detailed
specification of the OMNI interface adaptation layer mapping cache
for LLAs/MLAs and Source/Target Link Layer Address Options (S/
TLLAO).)
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AERO nodes assign a unique MLA to the OMNI interface per
[I-D.templin-6man-mla]. OMNI interface MLAs can use (Hierarchical)
Host Identity Tags ("(H)HITs") [RFC7343][RFC9374] or other special-
purpose IPv6 addresses as MLAs given sufficient uniqueness and
authorization assurance. The node assigns an MLA to an OMNI
interface the same as suggested for "sites" in the IPv6 scoped
addressing architecture [RFC4007], i.e., as a single adaptation layer
address assigned to a virtual interface configured over potentially
multiple underlying interfaces.
MLAs are considered as adaptation layer addresses in the
architecture, but nodes may also use them as the Source and
Destination Addresses of original IP packets exchanged between peers
in isolated MANETs with intermittent connection to the global
Internet. Each original IP packet with MLA addresses is subject to
OAL encapsulation with an IPv6 header that also uses MLA addresses.
AERO Clients receive Globally Unique Address (GUA) prefixes during
Proxy/Server RS/RA exchanges and configure per underlay interface GUA
addresses from the prefixes. AERO Clients also receive a Unique
Local Address (ULA) prefix fd00::/8 followed by a pseudo-random
40-bit Global ID to form the prefix {ULA}::/48, then include a 16-bit
Subnet ID '*' to form the prefix {ULA*}::/64 [RFC4291]. AERO Proxy/
Servers assign ULAs to Clients as *NET internal addresses in 1x1
correspondence with GUAs as *NET external addresses according to
NPTv6 [RFC6296].
AERO MSPs, MNPs, FNPs and SNPs are typically based on GUAs, but in
some cases may be based on IPv4 private addresses [RFC1918] or IPv6
ULA-C's [RFC4193].
AERO address selection rules are conducted per [RFC6724] as updated
by [I-D.ietf-6man-rfc6724-update].
AERO Clients and Proxy/Servers use their MLAs as OAL Source and
Destination Addresses within the FHS *NET. FHS Proxy/Servers rewrite
OAL MLA Source and Destination Addresses as SNP SRA GUAs before
forwarding packets over intervening Gateways on the paths to LHS
Proxy/Servers. LHS Proxy/Servers in turn rewrite OAL SNP SRA GUA
Source and Destination Addresses as MLAs for forwarding within the
LHS *NET.
See [I-D.templin-6man-omni3] for a full discussion of the various
unicast, anycast and multicast addresses used by AERO nodes on OMNI
links.
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4.2.3. AERO Routing System
The AERO routing system comprises a private Border Gateway Protocol
(BGP) [RFC4271] service coordinated between Gateways as interior
nodes and Proxy/Servers and Relays as leaf nodes of a spanning tree.
The service supports OAL packet/fragment forwarding at a layer below
IP and does not interact with the public Internet BGP routing system,
but supports redistribution of information for other networks
connected by Relays.
In a reference deployment, each Proxy/Server is configured as an
Autonomous System Border Router (ASBR) for a stub Autonomous System
(AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within
the BGP instance, and each Proxy/Server further uses eBGP to peer
with one or more Gateways but does not peer with other Proxy/Servers.
Each SRT segment in the OMNI link must include one or more Gateways
in a "hub" AS, which peer with the Proxy/Servers within that segment
as "spoke" ASes. All Gateways within the same segment are members of
the same hub AS, and use iBGP to maintain a consistent view of all
active routes currently in service. The Gateways of different
segments peer with one another using eBGP.
Gateways maintain forwarding table entries for the SNP prefixes
assigned to Proxy/Servers and the set of all FNP/MNP routes that are
currently active; Gateways also maintain black-hole routes for the
OMNI link MSPs so that OAL packets/fragments destined to non-existent
more-specific routes are flushed from the routing system. In this
way, Proxy/Servers and Relays have only partial topology knowledge
(i.e., they only maintain routing information for their directly
associated Clients and foreign links) and they forward all other OAL
packets/fragments to Gateways which have full topology knowledge.
Each OMNI link segment assigns a unique sub-prefix of the MSP known
as the "SRT prefix". For example, a first segment could assign
2001:db8::/48, a second could assign 2001:db8:1::/48, a third could
assign 2001:db8:2::/48, etc. Within each segment, each Proxy/Server
and Gateway configures an SNP within the segment's SRT prefix, e.g.,
the SNPs 2001:db8::/64, 2001:db8:0:1::/64 2001:db8:0:2::/64 all
belong to the SRT prefix 2001:db8::/48.
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The administrative authorities for each segment must therefore
coordinate to assure mutually-exclusive SNP assignments, but internal
provisioning of SNPs is an independent local consideration for each
administrative authority. For each SRT prefix, the Gateway(s) that
connect that segment assign the all-zero's address of the prefix as a
Subnet Router Anycast (SRA) address. For example, the SRA address
for 2001:db8::/48 is simply 2001:db8::. All Proxy/Servers also assign
the SRA address taken from their uniquely-assigned more-specific SNP,
e.g., the SRA address for the SNP 2001:db8:0:1::/64 is simply
2001:db8:0:1::.
SRT prefixes (and their SNP sub-prefixes) are statically represented
in Gateway forwarding tables. Gateways join multiple SRT segments
into a unified OMNI link over multiple diverse network administrative
domains. They support a virtual bridging service by first
establishing forwarding table entries for their SRT prefixes either
via standard BGP routing or static routes. For example, if three
Gateways ('A', 'B' and 'C') from different segments serviced
2001:db8::/48, 2001:db8:1::/48 and 2001:db8:2::/48 respectively, then
the forwarding tables in each gateway appear as follows:
A: 2001:db8::/48->local, 2001:db8:1::/48->B, 2001:db8:2::/48->C
B: 2001:db8::/48->A, 2001:db8:1::/48->local, 2001:db8:2::/48->C
C: 2001:db8::/48->A, 2000:db8:1::/48->B, 2001:db8:2::/48->local
These forwarding table entries rarely change, since they correspond
to fixed infrastructure elements in their respective segments.
FNP and MNP routes are instead dynamically advertised in the AERO
routing system by Proxy/Servers and Relays that provide anchor points
for their corresponding prefixes. For example, if three Proxy/
Servers ('D', 'E' and 'F') service the MNPs 2001:db8:1000:1::64/,
2001:db8:1000:2::/64 and 2001:db8:1000:2::/48 then the routing system
would include:
D: 2001:db8:1000:1::/64
E: 2001:db8:1000:2::/64
F: 2001:db8:1000:3::/64
A full discussion of the BGP-based routing system used by AERO is
found in [I-D.ietf-rtgwg-atn-bgp].
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4.2.4. Segment Routing Topologies (SRTs)
The distinct GUA prefixes in an OMNI link domain identify distinct
Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive
OMNI link overlay instance using a distinct set of GUAs, and emulates
a bridged campus LAN service for the OMNI link. In some cases (e.g.,
when redundant topologies are needed for fault tolerance and
reliability) it may be beneficial to deploy multiple SRTs that act as
independent overlay instances. A communication failure in one
instance therefore will not affect communications in other instances.
Each SRT is identified by a distinct GUA prefix and assigns an IPv6
SRA address used for OMNI interface determination in Safety-Based
Multilink (SBM) as discussed in [I-D.templin-6man-omni3]. Each OMNI
interface further applies Performance-Based Multilink (PBM)
internally.
The Gateways and Proxy/Servers of each independent SRT engage in BGP
peerings to form a spanning tree with the Gateways in non-leaf nodes
and the Proxy/Servers in leaf nodes. The spanning tree is configured
over both secured and unsecured underlay network paths. The secured
spanning tree is used to convey secured control messages (and
sometimes data message extensions) between Proxy/Servers and
Gateways, while the unsecured spanning tree forwards bulk data
messages and/or unsecured control messages.
Each SRT segment is identified by a unique GUA prefix used by all
Proxy/Servers and Gateways in the segment. Each AERO node must
therefore discover an SRT prefix that correspondents can use to
determine the correct segment, and must publish the SRT prefix in
IPv6 ND messages.
Note: The distinct GUA prefixes in an OMNI link domain can be carried
either in a common BGP routing protocol instance for all OMNI links
or in distinct BGP routing protocol instances for different OMNI
links. In some SBM environments, such separation may be necessary to
ensure that distinct OMNI links do not include any common
infrastructure elements as single points of failure. In other
environments, carrying the GUAs of multiple OMNI links within a
common routing system may be acceptable.
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4.2.5. Segment Routing For OMNI Link Selection
Original IPv6 sources can direct IPv6 packets/parcels to an AERO node
by including a standard IPv6 Segment Routing Header (SRH) [RFC8754]
with the IPv6 SRA address for the selected OMNI link as either the
IPv6 Destination Address or as an intermediate hop Address[i] within
the SRH. This allows the original source to determine the specific
OMNI link SRT an original IPv6 packet/parcel will traverse when there
may be multiple alternatives.
When an AERO node processes the SRH and forwards the original IPv6
packet/parcel to the correct OMNI interface, the OMNI interface
writes the next IPv6 Address[i] from the SRH into the IPv6
Destination Address and decrements Segments Left. If decrementing
would cause Segments Left to become 0, the OMNI interface deletes the
SRH before forwarding. This form of Segment Routing supports SBM.
4.3. OMNI Interface Characteristics
OMNI interfaces are virtual interfaces configured over one or more
underlay interfaces classified as follows:
* (M)ANET interfaces connect to a protected and secured ANET or an
open MANET that connects to an INET via Proxy/Servers. The
(M)ANET interface may be either on the same L2 link segment as a
Proxy/Server, or separated from a Proxy/Server by multiple IP
hops. (Note that NATs may appear internally within a (M)ANET and
may require NAT traversal on the path to the Proxy/Server the same
as for the INET case.) MANETs are special cases of ANETs in which
adaptation layer multihop forwarding may be necessary, and
protected secured underlay links cannot always be assumed.
* INET interfaces connect to an INET either natively or through one
or several IPv4 Network Address Translators (NATs). Native INET
interfaces have global IP addresses that are reachable from
correspondent on the same INET. NATed INET interfaces typically
have private IP addresses and connect to a private network behind
one or more NATs with the outermost NAT providing INET access.
* ENET interfaces connect a Client's downstream-attached networks,
where the Client provides forwarding services for ENET end system
communications to remote peers. An ENET can be as simple as a
small IoT sub-network that travels with a mobile Client to as
complex as a large private enterprise network that the Client
connects to a larger ANET or INET.
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* VPN interfaces use security encapsulations (e.g. IPsec tunnels)
over underlay networks to connect Clients, Proxy/Servers and/or
Gateways. VPN interfaces provide security services at lower
layers of the architecture (L2/L1) the same as for Direct point-
to-point interfaces.
* Direct point-to-point interfaces securely connect Clients, Proxy/
Servers and/or Gateways over physical or virtual media that does
not transit any open Internetwork paths. Examples include a line-
of-sight link between a remote pilot and an unmanned aircraft, a
fiberoptic link between Gateways, etc.
OMNI interfaces use OAL encapsulation and fragmentation as discussed
in Section 4.6. OMNI interfaces use L2 encapsulation (see:
Section 4.6) to exchange carrier packets with OMNI link neighbors
over INET interfaces and IPsec tunnels as well as over ANET
interfaces for which the Client and neighbor may be multiple IP hops
away. OMNI interfaces use link layer encapsulation only (i.e., and
no other L2 encapsulations) over Direct underlay interfaces or
(M)ANET interfaces when the Client and neighbor are known to be on
the same underlay link.
OMNI interfaces maintain an adaptation layer view of the neighbor
cache for tracking per-neighbor state. IP nodes that configure OMNI
interfaces use ND messages including Router Solicitation (RS), Router
Advertisement (RA), Neighbor Solicitation (NS), Neighbor
Advertisement (NA), unsolicited Neighbor Advertisement (uNA) and
Redirect to manage both the network and adaptation layer views of the
neighbor cache. The adaptation layer further uses a multilink
forwarding message set termed Multilink Initiate (MI), Multilink
Respond (MR) and Multilink Control (MC) which use the same ICMPv6
Type value as the standard NA message but with different Code values.
OMNI neighbors invoke per-flow OAL Identification window
synchronization in their ND message exchanges to enable Source
Address verification, header compression and robust fragmentation/
reassembly.
OMNI interfaces include OMNI options formatted as specified in
[I-D.templin-6man-omni3] in the IP ND messages they forward on behalf
of the network layer. The OMNI option includes prefix registration
information, Interface Attributes and/or Neighbor Synchronization
parameters for coordinating the OMNI interface's underlay interfaces.
A Client's OMNI interface may be configured over multiple *NET
underlay interfaces. For example, common mobile handheld devices
have both wireless local area network ("WLAN") and cellular wireless
links. These links are often used "one at a time" with low-cost WLAN
preferred and highly-available cellular wireless as a standby, but a
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simultaneous-use capability could provide benefits. In a more
complex example, aircraft frequently have many wireless data link
types (e.g. satellite-based, cellular, terrestrial, air-to-air
directional, etc.) with diverse performance and cost properties.
If a Client's multiple *NET underlay interfaces are used "one at a
time" (i.e., all other interfaces are in standby mode while one
interface is active), then successive IPv6 ND messages all include
OMNI option Interface Attributes, Traffic Selector and/or Neighbor
Synchronization sub-options with the same underlay interface ifIndex.
In that case, the Client would appear to have a single underlay
interface but with a dynamically changing link layer address.
If the Client has multiple active *NET underlay interfaces, then from
the perspective of IPv6 ND it would appear to have multiple link
layer addresses. In that case, IPv6 ND message OMNI options MAY
include sub-options with different underlay interface ifIndexes.
Proxy/Servers on the open Internet include only a single INET
underlay interface. INET Clients therefore discover only the L2ADDR
information for the Proxy/Server's INET interface. Proxy/Servers on
a (M)ANET/INET boundary include both (M)ANET and INET underlay
interfaces. (M)ANET Clients therefore must discover both the (M)ANET
and INET L2ADDR information for their Proxy/Servers.
Gateway and Proxy/Server OMNI interface connections to the SRT are
configured over both secured IPsec tunnels for carrying IPv6 ND and
BGP protocol control plane messages and open INET paths for carrying
unsecured data plane messages. The OMNI interface configures an MLA
and acts as an OAL source to encapsulate original IP packets/parcels,
then fragments the resulting OAL packets, performs L2 encapsulation/
fragmentation and sends the resulting carrier packets over the
secured or unsecured underlay paths. Note that Gateway and Proxy/
Server end-to-end transport protocol sessions used by the BGP run
directly over the OMNI interface and use MLA IPv6 Source and
Destination Addresses.
4.4. OMNI Interface Initialization
AERO Proxy/Servers and Clients configure OMNI interfaces as their
point of attachment to the OMNI link. AERO nodes assign the MSPs for
the link to their OMNI interfaces (i.e., as a "route-to-interface")
to ensure that original IP packets/parcels with Destination Addresses
covered by an MNP not explicitly associated with another interface
are directed to an OMNI interface.
OMNI interface initialization procedures for Gateways, Proxy/Servers
and Clients are discussed in the following sections.
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4.4.1. AERO Gateway Behavior
AERO Gateways configure an OMNI interface and assign both MLAs and
SNPs with corresponding SRA GUAs for their OMNI link SRT segments.
Gateways configure underlay interface secured tunnels with Proxy/
Servers in the same SRT segment and other Gateways in the same (or an
adjacent) SRT segment. Gateways then engage in an adaptation layer
BGP routing protocol session with neighbors over the secured spanning
tree (see: Section 4.2.3).
4.4.2. AERO Proxy/Server and Relay Behavior
When a Proxy/Server enables an OMNI interface, it assigns both an LLA
and MLA plus one or more SNP ULA/GUA prefix pairs. The Proxy/Server
then configures SRA GUAs appropriate for the given OMNI link SRT
segment externally and configures SRA ULAs appropriate for the
locally attached *NET internally. The Proxy/Server also configures
secured underlay interface tunnels and engages in adaptation layer
BGP routing protocol sessions over the OMNI interface with one or
more neighboring Gateways.
The OMNI interface provides a single interface abstraction to the
network layer, but internally serves as an NBMA nexus for exchanging
carrier packets with other OMNI nodes over underlay interfaces and/or
secured tunnels. The Proxy/Server further configures a service to
facilitate IPv6 ND exchanges with AERO Clients and manages per-Client
Neighbor Cache Entries (NCEs) and IP forwarding table entries based
on control message exchanges.
Relays are simply Proxy/Servers that run a dynamic routing protocol
to redistribute routes between the OMNI interface and foreign
networks/links (see: Section 4.2.3). The Relay provisions MNPs and
advertises the MSP(s) for the OMNI link over its foreign network
interface attachments. The Relay further provides an OMNI link
attachment point for FNP-based topologies.
4.4.3. AERO Client Behavior
When a Client enables an OMNI interface, it assigns an LLA and a
unique MLA to the OMNI interface. The Client then sends OMNI-
encapsulated RS messages to FHS Proxy/Servers which allocate an SNP
ULA/GUA address pair and optionally coordinate with a MAP Proxy/
Server that delegates one or more MNPs. The MAP/FHS Proxy/Servers
then return an RA message to the Client which may pass through one or
more NATs in the path.
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When the Client sends initial RS messages, it will discover ULAs/GUAs
in the corresponding RAs that it receives from FHS Proxy/Servers and
can then assign the ULAs/GUAs to the OMNI interface. If the Client
is operating outside the context of AERO infrastructure, however, it
may continue using MLAs over its underlay or OMNI interfaces for
peer-to-peer communications within the local *NET. The Client can
then continue indefinitely or at least until it encounters an
infrastructure element that can delegate SNP ULA/GUA pairs and/or
MNPs.)
A Client can further extend the OMNI link over its (downstream) ENET
interfaces where it provides a first-hop router for end systems and
other Clients connected to the ENET. A downstream Client that
connects via the ENET serviced by an upstream Client can in turn
service further downstream ENETs that connect other end systems and
Clients. This OMNI link extension can be applied recursively over a
"chain" of ENET Clients acting as Proxys.
4.5. OMNI Interface Neighbor Cache Maintenance
Each Client and Proxy/Server OMNI interface maintains a network layer
conceptual Neighbor and Destination Cache per [RFC1256][RFC4861] the
same as for any IP interface. The OMNI interface neighbor cache is
maintained through static and/or dynamic neighbor cache entry
configurations. The IP layer initiates and terminates IP ND
messaging exchanges to manage the network layer view of the neighbor
cache.
Each OMNI interface also maintains an internal adaptation layer view
of the neighbor cache that includes a Neighbor Cache Entry (NCE) for
each of its active OAL neighbors per [RFC4861]. IPv6 ND messages
that update the adaptation layer neighbor cache include an OMNI
option with zero or more sub-options.
Each OMNI interface NCE is indexed by the IPv6 MLA of a neighbor
found in an ND message and determines the context for Identification
verification. Clients and Proxy/Servers maintain NCEs through
dynamic RS/RA message exchanges, and also maintain NCEs for any
active correspondent peers through dynamic IPv6 ND message exchanges.
Clients establish NCEs for their associated FHS and MAP Proxy/Servers
through the exchange of RS/RA messages. When a Client and Proxy/
Server establish NCEs, they set a ReachableTime timer to
REACHABLE_TIME seconds. Clients determine the service profiles for
their FHS and MAP Proxy/Servers by setting the OMNI Neighbor
Synchronization sub-option NUD/ARR/RPT flags in RS messages and also
by setting/clearing the FMT-Forward and FMT-Mode flags in the
Interface Attributes sub-option. When the NUD/ARR/RPT flags are
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clear, Proxy/Servers forward all Address Resolution (NS/NA(AR)) and
Neighbor Unreachability Detection (NS/NA(NUD)) messages to the
Client, while the Client performs mobility update signaling through
the transmission of uNA messages to all active neighbors following a
mobility event. However, in some environments this may result in
excessive IPv6 ND control message overhead especially for Clients
connected to low-end data links.
Clients can therefore set the NUD/ARR/RPT flags in RS messages they
send to request their desired Proxy/Server service profiles. If the
NUD flag is set, the FHS Proxy/Server that forwards the RS message
assumes the role of responding to NS(AR/DAD) messages and maintains
peer NCEs associated with the NCE for this Client. If the ARR flag
is set, the MAP Proxy/Server that processes the RS message assumes
the role of responding to NS(AR) and NS(DAD) messages on behalf of
this Client NCE. If the RPT flag is set, the MAP Proxy/Server that
processes the RS message becomes responsible for maintaining a
"Report List" for each Client NCE for the Source Addresses of NS(AR)
messages it forwards or responds to on behalf of this Client.
When a Client sets the RPT flag, the MAP Proxy/Server maintains
Report List entries based on a ReportTime timer initialized to
REACHABLE_TIME seconds upon receipt of an NS(AR) and decremented once
per second while no additional NS(AR)s arrive. The MAP Proxy/Server
then sends uNA messages to each Report List entry when it receives a
Client mobility update indication (e.g., through receipt of an RS
with updated Interface Attributes and/or Traffic Selectors). When a
Report List entry ReportTime timer expires, the MAP Proxy/Server
deletes the entry. When a Client NCE timer expires, the MAP Proxy/
Server deletes the NCE along with its associated Report List.
Clients can also set/clear the FMT-Forward and FMT-Mode flags in the
Interface Attributes sub-option of each RS message to express their
desired service profile from each FHS Proxy/Server for a specific
underlay interface. The FHS Proxy/Server will consider the Client's
preferences and either accept or override by setting/clearing the
flags in the corresponding RA message reply. Implications for these
bit settings are discussed in [I-D.templin-6man-omni3].
Both the Client and its MAP Proxy/Server have full knowledge of the
Client's current underlay Interface Attributes and Traffic Selectors,
while FHS Proxy/Servers acting in "proxy" mode have knowledge of only
the individual Client underlay interfaces they service. Clients
request their desired FHS and MAP Proxy/Server service models by
setting the NUD/ARR/RPT flags in the RS messages they send as
discussed above.
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When an Address Resolution Source (ARS) sends an NS(AR) message
toward an Address Resolution Target (ART) Client/Relay, the OMNI link
routing system directs the NS(AR) to a MAP Proxy/Server for the ART.
The MAP then either acts as an Address Resolution Responder (ARR) on
behalf of the ART or forwards the NS(AR) to the ART which acts as an
ARR on its own behalf. The ARR returns an NA(AR) response to the
ARS, which creates or updates a NCE for the ART while caching L3 and
L2 addressing information. The ARS then (re)sets ReachableTime for
the NCE to REACHABLE_TIME seconds and performs multilink forwarding
ND message exchanges over specific underlay interface pairs to
determine paths for sending carrier packets directly to the ART. The
ARS otherwise decrements ReachableTime while no further solicited ND
messages arrive.
Proxy/Servers add an additional state DEPARTED to the list of NCE
states found in Section 7.3.2 of [RFC4861]. When a Client terminates
its association, the Proxy/Server OMNI interface sets a DepartTime
variable for the NCE to DEPART_TIME seconds. DepartTime is
decremented unless a new IPv6 ND message causes the state to return
to REACHABLE. While a NCE is in the DEPARTED state, the Proxy/Server
forwards OAL packets/fragments destined to the target Client to the
Client's new FHS/MAP Proxy/Server instead.
It is RECOMMENDED that REACHABLE_TIME be set to the default constant
value 30 seconds as specified in [RFC4861]. It is RECOMMENDED that
DEPART_TIME be set to the default constant value 10 seconds to accept
any carrier packets that may be in flight. When ReachableTime or
DepartTime decrement to 0, the NCE is deleted.
AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number
of NS(NUD) messages sent when a correspondent may have gone
unreachable, the value MAX_RTR_SOLICITATIONS to limit the number of
RS messages sent without receiving an RA and the value
MAX_NEIGHBOR_ADVERTISEMENT to limit the number of solicited IPv6 ND
advertisements that can be sent based on a single event. It is
RECOMMENDED that MAX_UNICAST_SOLICIT, MAX_RTR_SOLICITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the same as specified in
[RFC4861].
Different values for the above constants MAY be administratively set;
however, if different values are chosen, all nodes on the link MUST
consistently configure the same values.
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4.5.1. AERO/OMNI Control Plane Messages
OMNI interfaces use IPv6 ND messages as the secured control plane
messaging service for all adaptation layer neighbor coordination
exchanges. OMNI interfaces forward IPv6 ND messages to and from the
IP layer the same as for standard IPv6 ND, but during IPv6 ND message
encapsulation also append a trailing OMNI pseudo-option
[I-D.templin-6man-omni3].
For each IPv6 ND message, the OMNI interface includes a trailing OMNI
option following any other ND message options then completely
populates all sub-option information. If the OMNI interface includes
an Authentication sub-option, it calculates and includes a digital
signature per the OMNI specification. OMNI interfaces verify
integrity and authentication of each message received, and process
the message further only following successful verification.
OMNI options include per-neighbor information that provides multilink
forwarding, link layer address and traffic selector information for
the neighbor's underlay interfaces. This information is stored in
both the neighbor cache and AERO Forwarding Information Base (AFIB)
as basis for the forwarding algorithm specified in Section 4.10. The
information is cumulative and reflects the union of the OMNI
information from the most recent IPv6 ND messages received from the
neighbor.
The OMNI option is distinct from any IPv6 ND message options
including the Source/Target Link-Layer Address Option (S/TLLAO)
prepared according to the appropriate IPv6 over specific link layer
specification (e.g., [RFC2464]). The OMNI option pertains to the
adaptation layer to underlay interface address mappings while the S/
TLLAO pertains to the network layer to adaptation layer mapping. The
adaptation layer appends an OMNI option when it forwards an IPv6 ND
message from the network layer to external peers. The adaptation
layer translates the S/TLLAO into a local representation of the
address and removes the OMNI option when it forwards an IPv6 ND
message from external peers to the network layer.
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OMNI interface IPv6 ND messages may also include additional OMNI sub-
options. In particular, solicitation messages may include a Nonce
option if required for verification of advertisement replies. If an
OMNI IPv6 ND solicitation message includes a Nonce option, the
advertisement reply must echo the same Nonce. If an OMNI IPv6 ND
solicitation message includes a Timestamp option, the recipient must
also include a Timestamp option in its advertisement reply. All
unsolicited advertisement and redirect messages must include a
Timestamp option. (Note that the OMNI option itself includes Nonce
and Timestamp sub-options that will often be used instead of the
corresponding IPv6 ND options.)
AERO Clients send RS messages with Source Address set to their own
LLA and Destination Address set to link-scoped All-Routers multicast
address or the LLA of a Proxy/Server. The OMNI adaptation layer then
translates the LLAS to MLAs while using unicast or anycast OAL
addresses and appropriate L2 addresses. AERO Proxy/Servers respond
by returning RA messages with a unicast LLA Source Address that is
translated to the corresponding MLA by the adaptation layer. During
RS/RA exchanges, AERO Clients and Proxy/Servers include state
synchronization parameters to establish Identification windows and
other state.
AERO nodes use NS/NA messages as follows:
* NS/NA(AR) messages are used for address resolution. When an ARS
prepares an NS(AR) it sets the IPv6 Source Address to its LLA
which the OMNI interface rewrites as its MLA. The ARS also sets
the Target Address to the IP Destination Address of the invoking
packet and sets the Destination Address to the solicited-node
multicast address corresponding to the (unicast) Target Address.
After the ARS sends the NS(AR), an ARR with addressing information
for the ART returns a unicast NA(AR) that contains current,
consistent and authentic Target Address resolution information.
The ARR sets the NA(AR) Source Address to its OMNI interface LLA
(for translation to its MLA), sets the Destination Address to the
Source Address of the NS(AR) and sets the Target Address to the
Target Address of the NS(AR). NS/NA(AR) messages must be secured.
* Other NS/NA message exchanges are used to determine target
reachability (NS/NA(NUD)). The source sends an NS to the unicast
address of the target while optionally including an OMNI Neighbor
Synchronization sub-option naming a specific underlay interface
pair, and the target returns a responsive NA. NS/NA messages that
use an in-window sequence number and do not update any other state
need not include an authentication signature but must include an
IPv6 ND message and OMNI option checksum. NS/NA messages used to
establish or update NCE and/or AFIB state must be secured.
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* Unsolicted NA messages (uNAs) are used to update a neighbor's
cache when an underlay interface address changes due to a mobility
event. Nodes also use uNAs during Route Optimization.
* NS/NA(DAD) messages are not used in AERO, since Duplicate Address
Detection is not supported on OMNI links.
AERO introduces three special-purpose IPv6 ND messages for Multilink
Forwarding. These messages use the same Type value and message
formatting specifications as the standard NA messages but include
different Code values. The messages are:
* Multilink Initiate (MI) (Type 136; Code TBD1) - sent as an
adaptation layer control message used to initiate state needed to
support multilink forwarding. Recipients of MI messages respond
by returning a Multilink Respond (MR).
* Multilink Respond (MR) (Type 136; Code TBD2) - an adaptation layer
control message multilink forwarding response to an MI message.
Recipients of MR messages optionally return a Multilink Control
(MC).
* Multilink Control (MC) (Type 136; Code TBD3) - a muti-purpose
secured standalone adaptation layer control message used to
confirm a previous MI/MR exchange, establish multilink forwarding
state, forward error/informational messages or transport passenger
packets.
Unlike standard IPv6 ND messages, the pseudo message set (MI/MR/MC)
is used internally within the adaptation layer only and the messages
are never exposed to the network layer; any MI/MR/MC messages
accidentally exposed to the network layer would be silently discarded
due to RS message validation rules per [RFC4861] since they include
non-zero Code values.
IPv6 ND (pseudo) messages sent on OMNI links that must be examined by
transit OAL intermediate systems on the path require a special
codepoint for recognition other than the IPv6 Destination Address.
The OAL source therefore sets the DSCP field in the IPv6 OAL
encapsulation header of such messages to the special value '111111'
(see: [I-D.templin-6man-omni3]). The control planes of transit OAL
intermediate systems can then intercept and process these messages
before forwarding them to the next OAL hop.
IPv6 ND (pseudo) messages that require explicit multihop routing
guidance include an OMNI Routing Header (ORH)
[I-D.templin-6man-omni3] extension to the OAL IPv6 header that
includes the AFVI and optionally an LHS Client or Proxy/Server IPv6
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GUA and the IPv6 MLA of the OAL end system that serves the final
destination. The ORH then guides the forwarding algorithm for OMNI
link traversal.
IPv6 ND pseudo messages MI and MC set the Target Address to the
Source Address of the subject packet, set the Source Address to the
MLA of the source peer and set the Destination Address to the
Destination Address of the subject packet. IPv6 ND pseudo message MR
sets the Target Address to the Destination Address of the subject
packet, sets the Source Address to the MLA of the target peer and
sets the Destination Address to the Source Address of the subject
packet.
IPv6 ND pseudo messages include the MLA of the peer in an ORH
extension to the OAL IPv6 header. The IPv6 ND pseudo message R/S/O
flags are unused; they should be set to 0 on transmission and ignored
on reception.
4.5.2. OMNI Neighbor Window Synchronization
In secured environments (e.g., between secured spanning tree
neighbors, between neighbors on the same secured ANET, etc.), OMNI
interface neighbors can exchange AERO control messages without
including Identification values. In environments where spoofing is
considered a threat, OMNI interface neighbors instead invoke
Identification window synchronization by including OMNI Neighbor
Synchronization sub-options in IPv6 ND message exchanges to maintain
send/receive window state in their respective neighbor caches as well
as in AFIB entries of all OAL intermediate nodes in the forward and
reverse paths.
In common arrangements, OAL Identification window synchronization is
necessary for Client to Client, Client to Proxy/Server or Proxy/
Server to Proxy/Server message exchanges conducted over unsecured
Internetwork paths. Conversely, Proxy/Server to Proxy/Server, Proxy/
Server to Gateway and Gateway to Gateway message exchanges carried
over the secured spanning tree do not require window synchronization.
OAL end system and intermediate nodes verify Identification values of
OAL packets that traverse the unsecured spanning tree according to
their populated AFIB state. This allows each OAL node to exclude
spurious packets injected into the OMNI link from an off-path
adversary.
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4.6. OMNI Interface Encapsulation and Fragmentation
When the network layer forwards an original IP packet/parcel into an
OMNI interface, the interface locates a NCE corresponding to the OAL
destination. The OMNI interface then invokes the OAL as discussed in
[I-D.templin-6man-omni3] which removes the virtual Ethernet header
and encapsulates the packet/parcel in an IPv6 header to form an OAL
packet.
Following encapsulation, the OAL source then fragments the OAL packet
while including an identical Identification value for each fragment
that must be within the window for the flow over the interface pair
selected for the neighbor. The OAL source includes any necessary OAL
IPv6 extension headers including an identical OMNI Routing Header
(ORH) [I-D.templin-6man-omni3] with each fragment ORH containing an
AERO Forwarding Vector Index (AFVI) as discussed in Section 4.13.
The OAL source can instead invoke OAL header compression by replacing
the full OAL IPv6 header (OFH), ORH and Extended Fragment Header with
an OAL Compressed Header (OCH) (see: [I-D.templin-6man-omni3]).
For messages that will traverse unsecured paths, the OAL source
finally performs L2 encapsulation/fragmentation on each resulting OAL
fragment to form a carrier packet, with Source Address set to its own
L2 address (e.g., 192.0.2.100) and Destination Address set to the L2
address of the next hop OAL intermediate system or destination (e.g.,
192.0.2.1). The carrier packet encapsulation format in the above
example is shown in Figure 3:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 Headers |
~ src = 192.0.2.100 ~
| dst = 192.0.2.1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ L2 IPv6 Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL IPv6 Header |
~ Source Address (1) ~
| Destination Address (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ OAL IPv6 Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original IP Header |
~ (first-fragment only) ~
~ Source Address (3) ~
| Destination Address (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Original Packet Body/Fragment ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Carrier Packet Format
In this format, the OAL source encapsulates the original IP header
and packet/parcel body/fragment in an OAL IPv6 header. The OAL
source then adds an ORH plus Extended Fragment Header as OAL IPv6
header extensions for each fragment and prepends L2 headers prepared
as discussed in [I-D.templin-6man-omni3]. The OAL source sends each
such carrier packet into the SRT unsecured spanning tree, where they
may be forwarded over multiple OAL intermediate systems until they
arrive at the OAL destination. These carrier packets may themselves
be subject to L2 fragmentation and reassembly along the concatenated
path segments.
The OMNI link control plane service distributes Client MNP prefix
information that may change occasionally due to regional node
mobility, as well as more static information for Relay FNPs and per-
segment SNPs that rarely change. OMNI link Gateways and Proxy/
Servers use the information to establish and maintain a forwarding
plane spanning tree that connects all nodes on the link. The
spanning tree supports a virtual bridging service according to link
layer (instead of network layer) information, but may often include
longer paths than necessary.
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Each OMNI interface therefore also includes an AERO Forwarding
Information Base (AFIB) that caches AERO Forwarding Vectors (AFVs)
which can provide both carrier packet Identification context and more
direct forwarding "shortcuts" that avoid strict spanning tree paths.
As a result, the spanning tree is always available but OMNI
interfaces can often use the AFIB entries established through route
optimization to greatly improve performance and reduce load on
critical infrastructure elements.
For OAL packets/fragments undergoing L2 re-encapsulation at an OAL
intermediate system, the OMNI interface performs L2 reassembly/
decapsulation followed by Identification verification and OAL
reassembly only if the OAL packet/fragment is addressed to itself.
The OMNI interface then decrements the OAL IPv6 header Hop Limit and
discards the packet/fragment if the Hop Limit reaches 0. Otherwise,
the OMNI interface updates the OAL addresses if necessary, includes
an appropriate Identification, performs OAL fragmentation then for
each OAL fragment performs L2 encapsulation/fragmentation to produce
carrier packets appropriate for next segment forwarding.
4.7. OMNI Interface Decapsulation
When an OAL node receives OAL packets/fragments addressed to another
node, it discards the L2 headers and includes new L2 headers
appropriate for the next hop in the forwarding path to the OAL
destination (after first performing any necessary L2 fragmentation or
reassembly). The node then sends these new carrier packets into the
next hop underlay interface.
When an OAL node receives OAL packets/fragments addressed to itself,
it performs L2 reassembly/decapsulation, verifies the Identification,
then performs OAL reassembly/decapsulation to obtain the original OAL
packet or composite packet (see: [I-D.templin-6man-omni3]). Next, if
the enclosed original IP packet(s)/parcel(s) are addressed either to
itself or to a destination reached via an interface other than the
OMNI interface, the OAL node replaces the OAL encapsulation IPv6
header with a virtual Ethernet header and forwards the original IP
packet(s)/parcel(s) to the network layer.
If the original IP packet(s)/parcel(s) are destined to another node
reached by the OMNI interface, the OAL node instead changes the OAL
Source Address to its own address, changes the OAL Destination
Address to the address of the next-hop node over the OMNI interface,
decrements the Hop Limit, then performs L2 encapsulation/
fragmentation and forwards these new carrier packets into an underlay
interface for the next segment.
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Further OMNI link decapsulation details are specified in
[I-D.templin-6man-omni3]. Further OMNI link forwarding procedures
are specified in Section 4.10.
4.8. OMNI Interface Data Origin Authentication
AERO nodes employ simple data origin authentication procedures. In
particular:
* AERO Gateways and Proxy/Servers accept carrier packets received
from the secured spanning tree.
* AERO Proxy/Servers and Clients accept carrier packets and original
IP packets/parcels that originate from within the same secured
ANET.
* AERO Clients and Relays accept original IP packets/parcels from
downstream network correspondents based on ingress filtering.
* AERO Clients, Relays, Proxy/Servers and Gateways verify carrier
packet L2 encapsulation addresses according to
[I-D.templin-6man-omni3].
* OAL end systems and intermediate systems forward/accept OAL
packets/fragments with Identification values within the current
window for the OAL source neighbor for a specific underlay
interface pair and drop any packets with out-of-window
Identification values.
AERO nodes silently drop any packets/parcels that do not satisfy the
above data origin authentication procedures. Further security
considerations are discussed in Section 7.
4.9. OMNI Interface MTU
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Effective MTU to Receive (EMTU_R)
and the role of fragmentation and reassembly
[I-D.ietf-intarea-tunnels]. The OMNI interface employs the OAL to
accommodate multiple underlay links with diverse MTUs. OMNI
interface packet sizing considerations are specified in
[I-D.templin-6man-omni3], where the OMNI interface MTU can
essentially be considered "unlimited".
When the network layer presents an original IP packet/parcel to the
OMNI interface, the OAL source encapsulates and fragments the packet/
parcel if necessary. When the network layer presents the OMNI
interface with multiple original IP packets/parcels addressed to the
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same IPv6 flow, the OAL source can concatenate them as a single OAL
composite packet as discussed in [I-D.templin-6man-omni3] before
applying fragmentation. The OAL source then submits each OAL
fragment for L2 encapsulation/fragmentation for transmission as
carrier packets over an underlay interface connected to either a
physical link (e.g., Ethernet, WiFi, Cellular, etc.) or a virtual
link such as an Internet or higher-layer tunnel.
4.10. OMNI Interface Forwarding Algorithm
Original IP packets/parcels enter a node's OMNI interface either from
the network layer (i.e., from a local application or the IP
forwarding system) while carrier packets enter from the link layer
(i.e., from an OMNI interface neighbor). All original IP packets/
parcels and carrier packets entering a node's OMNI interface first
undergo data origin authentication as discussed in Section 4.8.
Those that satisfy data origin authentication are processed further,
while all others are dropped silently.
Original IP packets/parcels that enter the OMNI interface from the
network layer are forwarded to an OMNI interface neighbor using OAL
encapsulation and fragmentation to produce carrier packets for
transmission over underlay interfaces. (If forwarding state
indicates that the original IP packet/parcel should instead be
forwarded back to the network layer, the packet/parcel is dropped to
avoid looping). Carrier packets that enter the OMNI interface from
the link layer are either re-encapsulated and re-admitted into the
link layer, or reassembled and forwarded to the network layer where
they are subject to either local delivery or IP forwarding.
When the network layer of a router forwards an original IP packet/
parcel into the OMNI interface, it decrements the TTL/Hop Limit
following standard IP router conventions. Once inside the OMNI
interface, however, the OAL does not further decrement the original
IP packet/parcel TTL/Hop Limit since its adaptation layer forwarding
actions occur below the network layer. The original IP packet/
parcel's TTL/Hop Limit will therefore be the same when it exits the
destination OMNI interface as when it first entered the source OMNI
interface.
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When an OAL intermediate system receives a carrier packet, it
performs L2 reassembly/decapsulation to obtain the enclosed OAL
packet/fragment. When the intermediate system forwards an OAL
packet/fragment not addressed to itself (or one addressed to itself
but that also includes an ORH with Segments Left greater than 0), it
decrements the OAL Hop Limit without decrementing the network layer
IP TTL/Hop Limit. If decrementing would cause the OAL Hop Limit to
become 0, the OAL intermediate system drops the OAL packet/fragment.
This ensures that original IP packet(s)/parcel(s) cannot enter an
endless loop.
OMNI interfaces may have multiple underlay interfaces and/or NCEs for
neighbors with multiple underlay interfaces (see Section 4.3). The
OAL uses Interface Attributes and/or Traffic Selectors to select an
outbound underlay interface for each OAL packet and also to select
segment routing and/or link layer Destination Addresses based on the
neighbor's target underlay interfaces. AERO implementations SHOULD
permit network management to dynamically adjust Traffic Selector
values at runtime.
If an OAL packet/fragment matches the Interface Attributes and/or
Traffic Selectors of multiple outgoing interfaces and/or neighbor
interfaces, the OMNI interface replicates the packet and sends a
separate copy via each of the (outgoing / neighbor) interface pairs;
otherwise, it sends a single copy via an interface with the best
matching attributes/selectors. (While not strictly required, the
likelihood of successful reassembly may improve when the OMNI
interface sends all fragments of the same fragmented OAL packet/
fragment consecutively over the same underlay interface pair to avoid
complicating factors such as delay variance and reordering.) AERO
nodes keep track of which underlay interfaces are currently
"reachable" or "unreachable", and use only "reachable" interfaces for
forwarding purposes.
In addition to standard forwarding based on Interface Attributes and/
or Traffic Selectors, nodes may employ a policy engine that would
provide further guidance to the forwarding algorithm. For example
the policy engine may suggest a load balancing profile over multiple
underlay interface pairs, with portions of a traffic flow spread
between multiple paths according to Equal Cost MultiPath or Link
Aggregation Groups (LAGs) [RFC6438] (note that Interface Attributes
include an underlay interface group identifier). Other policies may
suggest the use of paths with the least cost, best performance, etc.
This document therefore specifies mechanisms without mandating any
particular policies.
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All Clients, Proxy/Servers and Gateways serve as OAL intermediate
nodes for the purpose of forwarding OAL packets/fragments that
include an ORH or OCH with non-zero AFVI over the unsecured spanning
tree based on AFIB entries. When an OAL intermediate node forwards
an OAL packet/fragment with an L2 Source Address and AFVI that
matches an AFV, the node first verifies that the Identification is in
sequence. The OAL intermediate node then rewrites the packet's AFVI
with a value that will be recognized by the next OAL hop and forwards
the packet. (For OAL packets/fragments with uncompressed headers and
with AFVI set to 0, the OAL intermediate node instead forwards based
on matching the OAL IPv6 Destination Address with a standard IPv6
forwarding table entry after applying ORH processing if necessary.)
The chain of OAL source, intermediate and destination nodes may
therefore traverse many Clients, Proxy/Servers and Gateways on the
path.
The following sections discuss the OMNI interface-specific forwarding
algorithms for Clients, Proxy/Servers and Gateways. In the following
discussion, an original IP packet/parcel's Destination Address is
said to "match" if it is the same as a cached address, or if it is
covered by a cached FNP/SNP/MNP.
4.10.1. Client Forwarding Algorithm
When an original IP packet/parcel enters a Client's OMNI interface
from the network layer the Client searches for a NCE that matches the
corresponding OAL destination. If there is a matching NCE for a
neighbor reached via a *NET interface (i.e., an upstream interface),
the Client selects one or more "reachable" neighbor interfaces in the
entry for forwarding purposes. Otherwise, the Client performs OAL
encapsulation and fragmentation if necessary, forwards the resulting
OAL packet/fragments to an FHS Proxy/Server, then either invokes
address resolution and multilink forwarding procedures per
Section 4.13 or allows the FHS Proxy/Server to invoke these
procedures on its behalf. If there is a matching NCE for a neighbor
reached via an ENET interface (i.e., a downstream interface), the
Client instead forwards the original IP packet/parcel to the
downstream end system or Client using L2 encapsulation and
fragmentation if necessary.
When a carrier packet enters a Client's OMNI interface from the link
layer, the Client performs L2 reassembly/decapsulation if necessary
to obtain the OAL packet/fragment then examines the OAL Destination
Address (i.e., after locating the correct AFV if the OAL packet
header is OCH). If the OAL Destination Address matches one of the
Client's addresses and the packet includes an ORH with Segments Left
greater than 0, the Client rewrites the OAL Destination Address and
forwards the packet to the peer Client indicated by the next hop ORH
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Address[i]. Otherwise, the Client (acting as an OAL destination)
verifies that the Identification is in-window for the matching AFV,
then reassembles/decapsulates as necessary and delivers the original
IP packet/parcel to the network layer. If the OAL Destination
Address does not match, the Client drops the original IP packet/
parcel and MAY return a network layer ICMP Destination Unreachable
message subject to rate limiting (see: Section 4.11).
Note: The forwarding table entries established in peer Clients are
based on MLAs which also appear as OAL Source and Destination
Addresses within (M)ANETs but may be rewritten as GUAs over INETs.
The original IP packet Source and Destination Addresses instead use
LLAs, ULAs or GUAs. When ULAs are used, the subnet ID in the ULA /64
prefix provides topological relevance for the multihop forwarding
region, while the 64-bit Interface Identifier encodes the 1x1 mapping
of the MANET-internal ULA to the MANET-external GUA maintained by the
Proxy/Server that configures the ULA/GUA SNP.
Note: Clients within MANETs support Client-to-Client multihop
forwarding when necessary to reach destinations or FHS Proxy/Servers
that may be multiple OAL hops away. In this way, forwarding Clients
act as OAL intermediate nodes and forward using OCH compression based
on AFV state that is indexed by the AFVIs included in each OAL
packet/fragment. ULA-based communications are sufficient for Client-
to-Client communications within a MANET, while packets that enter or
exit the MANET via a FHS Proxy/Server may be subject to NPTv6
[RFC6296].
4.10.2. Proxy/Server and Relay Forwarding Algorithm
When the network layer admits an original IP packet/parcel into a
Proxy/Server's OMNI interface, the OAL drops the packet/parcel to
avoid looping if forwarding state indicates that it should be
forwarded back to the network layer. Otherwise, the OAL examines the
IP Destination Address to determine if it matches the SNP SRA GUA of
a neighboring Gateway found in the OMNI interface's network layer
neighbor cache. If so, the Proxy/Server performs OAL encapsulation
and fragmentation then performs L2 encapsulation/fragmentation and
forwards the resulting carrier packets to the Gateway over a secured
link (e.g., an IPsec tunnel, Direct link, etc.) to support control
plane functions such as the operation of the BGP routing protocol.
If the IP Destination Address matches an FNP/MNP associated with a
(foreign) Proxy/Server or Client, the (local) Proxy/Server instead
assumes the Relay role and forwards the original IP packet/parcel in
the same manner as for Client forwarding. Specifically, if there is
a matching NCE the Proxy/Server selects one or more "reachable"
neighbor interfaces in the entry for forwarding purposes; otherwise,
the Proxy/Server performs OAL encapsulation/fragmentation followed by
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L2 encapsulation/fragmentation and forwards the resulting carrier
packets while invoking address resolution and multilink forwarding
procedures per Section 4.13.
When the Proxy/Server receives/reassembles carrier packets on
underlay interfaces that contain OAL packets/fragments with both a
Source and Destination OAL Address that correspond to the same
Client's MLA, the Proxy/Server drops the carrier packets regardless
of their OMNI link point of origin. The Proxy/Server also drops
original IP packets/parcels received on underlay interfaces either
directly from a (M)ANET Client or following reassembly of carrier
packets received from a *NET Client if the original IP Destination
Address corresponds to the same Client's delegated MNP or SNP ULA/
GUA. Proxy/Servers also drop carrier packets that contain OAL
packets/fragments with foreign OAL Destination Addresses (MLAs) that
do not match one of their local *NET Clients. These checks are
essential to prevent forwarding inconsistencies from accidentally or
intentionally establishing endless loops that could congest nodes
and/or *NET links.
Proxy/Servers process carrier packets that contain OAL packets/
fragments with OCH headers or with Destination Addresses that match
their SNP ULA/GUA prefix or MLA and also include an ORH with AFVI and
possibly also Address[i] information. The Proxy/Server examines the
L2 Source Address and AFVI to locate the corresponding AFV entry in
the AFIB. The Proxy/Server then forwards them according to the AFV
state while decrementing the OAL packet/fragment Hop Limit.
For OAL packets/fragments with Destination Addresses that match their
MLA or SNP SRA prefix and also include an ORH, the Proxy/Server
performs any necessary local processing then rewrites the OAL
Destination Address according to the next hop ORH Address[i]. For
those that do not include an OCH or ORH with additional next hop
addresses, the Proxy/Server instead performs L2 reassembly/
decapsulation, verifies the Identification and performs OAL
reassembly to obtain the original IP packet/parcel. For data
packets/parcels addressed to its own SNP SRA GUA that arrived via the
secured spanning tree, the Proxy/Server delivers the original IP
packet/parcel to the network layer to support secured BGP routing
protocol control messaging. For data packets/parcels originating
from one of its dependent Clients, the Proxy/Server instead performs
OAL encapsulation/fragmentation followed by L2 encapsulation/
fragmentation and sends the resulting carrier packets while invoking
address resolution and multilink forwarding procedures per
Section 4.13. For IPv6 ND control messages, the Proxy/Server instead
authenticates the message and processes it as specified in later
sections of this document while updating neighbor cache and/or AFIB
state accordingly.
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When the Proxy/Server reassembles carrier packets that contain OAL
packets with OAL Destination Address set to an MLA or SNP ULA/GUA of
one of its Client neighbors established through RS/RA exchanges, it
accepts the carrier packets only if data origin authentication
succeeds. If the NCE state is DEPARTED, the Proxy/Server changes the
OAL Destination Address to the SNP SRA GUA of the new Proxy/Server,
decrements the OAL Hop Limit, then performs L2 encapsulation/
fragmentation and forwards the resulting carrier packets into the
spanning tree which will eventually deliver them to the new Proxy/
Server. If the neighbor cache state for the Client is REACHABLE and
the Proxy/Server is a MAP responsible for serving as the Client's
address resolution responder and/or default router, it verifies the
Identification then submits the OAL packet/fragment for reassembly.
The Proxy/Server then decapsulates and processes the resulting IPv6
ND message or original IP packet/parcel accordingly. Otherwise, the
Proxy/Server decrements the OAL Hop Limit, performs L2 encapsulation/
fragmentation and forwards the carrier packets to the Client which
then performs data origin verification and reassembly. (In the
latter case, the Client may receive fragments of the same original IP
packet/parcel from different Proxy/Servers but this will not
interfere with correct reassembly.)
When the Proxy/Server reassembles carrier packets that contain OAL
packets with OAL Destination Address set to a FNP address that does
not match the MSP, it accepts the carrier packets only if data origin
authentication succeeds and if there is a network layer forwarding
table entry for the FNP. The Proxy/Server then performs L2
reassembly/decapsulation, verifies the Identification, performs OAL
reassembly/decapsulation to obtain the original IP packet/parcel,
then presents it to the network layer (as a Relay) where it will be
delivered according to standard IP forwarding.
When a Proxy/Server receives a carrier packet from the secured
spanning tree, it considers the message as authentic without having
to verify network or higher layer authentication signatures.
If the Proxy/Server has multiple original IP packets/parcels to send
to the same neighbor, it can concatenate them as a single OAL
composite packet [I-D.templin-6man-omni3].
4.10.3. Gateway Forwarding Algorithm
When the network layer admits an original IP packet/parcel into the
Gateway's OMNI interface, the OAL drops the packet if routing
indicates that it should be forwarded back to the network layer to
avoid looping. Otherwise, the Gateway examines the IP Destination
Address to determine if it matches the SNP SRA GUA of a neighboring
Gateway or Proxy/Server by examining the OMNI interface's network
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layer neighbor cache. If so, the Gateway performs OAL encapsulation/
fragmentation followed by L2 encapsulation/fragmentation and forwards
the resulting carrier packets to the neighboring Gateway or Proxy/
Server over a secured link (e.g., an IPsec tunnel, etc.) to support
the operation of control plane functions (including the BGP routing
protocol) between OAL neighbors.
Gateways forward OAL packets/fragments reassembled from spanning tree
carrier packets while decrementing the OAL Hop Limit but not the
original IP header TTL/Hop Limit. Gateways send carrier packets that
contain OAL packets/fragments with critical IPv6 ND control messages
or BGP routing protocol control messages via the SRT secured spanning
tree, and may send other carrier packets via the secured/unsecured
spanning tree or via more direct paths according to AFIB information.
When the Gateway receives a carrier packet, it reassembles/
decapsulates to obtain the OAL packet/fragment then searches for an
AFIB entry that matches the OAL AFVI or an IPv6 forwarding table
entry that matches the OAL Destination Address.
Gateways process carrier packets containing OAL packets/fragments
with OAL Destination Addresses that do not match their SNP/SRT SRA
GUA in the same manner as for traditional IP forwarding within the
OAL, i.e., they forward packets not explicitly addressed to
themselves. Gateways locally process OAL packets/fragments with OCH
headers or full OAL headers with their SNP/SRT SRA GUA as the OAL
Destination Address. If the OAL packet/fragment contains an OCH or a
full OAL header with an ORH extension, the Gateway examines the AFVI
to locate the AFV entry in the AFIB for next hop forwarding. If an
AFV is found, the Gateway uses the next hop AFVI to forward the OAL
packet/fragment to the next hop while decrementing the OAL Hop Limit
but without reassembling. When the Gateway forwards the OAL packet/
fragment, it rewrites the OCH/ORH AFVI with the value it will
represent to the next OAL hop.
If the OAL packet/fragment includes a full OAL header but does not
include an AFVI, the Gateway instead examines the OAL packet. The
Gateway first determines whether the OAL packet includes an MI/MR/MC
message then processes the message according to the multilink
forwarding procedures discussed in Section 4.13. If the carrier
packets arrived over the secured spanning tree and the enclosed OAL
packets/fragments are addressed to its SNP/SRT SRA GUA, the Gateway
instead reassembles then discards the OAL header and forwards the
original IP packet/parcel to the network layer to support secured BGP
routing protocol control messaging. The Gateway instead drops all
other OAL packets.
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Gateways forward OAL packets/fragments received in carrier packets
that arrived from a first segment via the secured spanning tree to
the next segment also via the secured spanning tree. Gateways
forward OAL packets/fragments received in carrier packets that
arrived from a first segment via the unsecured spanning tree to the
next segment also via the unsecured spanning tree. Gateways
configure a single IPv6 routing table that determines the next hop
for a given OAL Destination Address, where the secured/unsecured
spanning tree is determined through the selection of the underlay
interface to be used for transmission (e.g., an IPsec tunnel or an
open INET interface).
As for Proxy/Servers, Gateways must verify that the L2 Source
Addresses of carrier packets not received from the secured spanning
tree are "trusted" before forwarding according to an AFV (otherwise,
the carrier packet must be dropped).
4.11. OMNI Interface Error Handling
When an AERO node admits an original IP packet/parcel into the OMNI
interface, it may receive link and/or network layer error
indications. The AERO node may also receive OMNI link error
indications in OAL-encapsulated MC messages that include
authentication signatures.
A link layer error indication is an ICMP error message generated by a
router in an underlay network on the path to the next OAL hop or by
the next OAL hop itself. The message includes an IP header with the
address of the node that generated the error as the Source Address
and with the link layer address of the AERO node as the Destination
Address.
The IP header is followed by an ICMP header that includes an error
Type, Code and Checksum. Valid type values include "Destination
Unreachable", "Packet Too Big", "Time Exceeded", "Parameter Problem"
etc. [RFC0792][RFC4443].
The ICMP header is followed by the leading portion of the carrier
packet that generated the error, also known as the "packet-in-error".
For ICMPv6, [RFC4443] specifies that the packet-in-error includes:
"As much of invoking packet as possible without the ICMPv6 packet
exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For
ICMPv4, [RFC0792] specifies that the packet-in-error includes:
"Internet Header + 64 bits of Original Data Datagram", however
[RFC1812] Section 4.3.2.3 updates this specification by stating: "the
ICMP datagram SHOULD contain as much of the original datagram as
possible without the length of the ICMP datagram exceeding 576
bytes".
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The link layer error message format is shown in Figure 4:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IP Header of link layer ~
~ error message ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ICMP Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| | P
~ carrier packet L2 and OAL ~ a
~ encapsulation headers ~ c
| | k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e
| | t
~original IP packet/parcel hdrs ~
~ (first-fragment only) ~ i
| | n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | e
~ Portion of the body of ~ r
~ the original IP packet/parcel ~ r
~ (all fragments) ~ o
| | r
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 4: OMNI Interface Link-Layer Error Message Format
The AERO node rules for processing these link layer error messages
are as follows:
* When an AERO node receives a link layer Parameter Problem message,
it processes the message the same as described as for ordinary
ICMP errors in the normative references [RFC0792][RFC4443].
* When an AERO node receives persistent link layer Packet Too Big
messages, there may be a restricting link on the path or the next
OAL hop may be experiencing reassembly cache congestion. In both
cases, the node should adaptively decrease the size of the OAL
fragments it sends to this OAL next hop (note that the PTB
messages could indicate either "hard" or "soft" errors).
* When an AERO node receives persistent link layer Time Exceeded
messages, the IP ID field may be wrapping before earlier fragments
awaiting reassembly have been processed. In that case, the node
should adaptively decrease the size of the OAL fragments it sends
to this OAL next hop.
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* When an AERO node receives persistent link layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor correspondents, the node should process the
message as an indication that a path may be failing, and
optionally initiate NUD over that path. If it receives
Destination Unreachable messages over multiple paths, the node
should allow future carrier packets destined to the correspondent
to flow through a default route and re-initiate route
optimization.
* When an AERO Client receives persistent link layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor Proxy/Servers, the Client should mark the
path as unusable and use another path. If it receives Destination
Unreachable messages on many or all paths, the Client should
associate with a new Proxy/Server and release its association with
the old Proxy/Server as specified in Section 4.15.5.
* When an AERO Proxy/Server receives persistent link layer
Destination Unreachable messages in response to carrier packets
that it sends to one of its neighbor Clients, the Proxy/Server
should mark the underlay path as unusable and use another underlay
path.
* When an AERO Proxy/Server receives link layer Destination
Unreachable messages in response to a carrier packet that it sends
to one of its permanent neighbors, it treats the messages as an
indication that the path to the neighbor may be failing. However,
the dynamic routing protocol should soon re-converge and correct
the temporary outage.
When an AERO Gateway receives a carrier packet for which the network
layer Destination Address is covered by an MSP assigned to a black-
hole route, the Gateway drops the carrier packet if there is no more-
specific routing information for the destination and returns an OMNI
interface Destination Unreachable message subject to rate limiting.
AERO nodes include ICMPv6 error messages intended for an OAL source
as sub-options in the OMNI option of secured MC messages. When the
OAL source receives the MC message, it can extract the ICMPv6 error
message enclosed in the OMNI option and either process it locally or
translate it into a network layer error to return to the original
source.
An AERO/OMNI intermediate system may discover that a transit packet
has no matching AFIB state to support forwarding to the next
adaptation layer hop. In that case, the intermediate system should
return a Destination Unreachable error sub-option in a secured MC
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message. The OAL source should process the message as an indication
that AFIB multilink forwarding state for a particular flow must be
refreshed.
4.12. AERO Mobility Service Coordination
AERO nodes observes the Router Discovery and Prefix Registration
specifications found in [I-D.templin-6man-omni3]. AERO nodes further
coordinate their autoconfiguration actions with the mobility service
as discussed in the following sections.
4.12.1. AERO Service Model
Each AERO Proxy/Server on the OMNI link is configured to respond to
Client address delegation requests for Provider Aggregated (PA)
addressing. Each Proxy/Server aggregates a unique PA prefix that it
does not coordinate with other Proxy/Servers, and ensures that only
unique PA addresses are delegated to requesting Clients. Each Proxy/
Server runs its own independent DHCPv6 server that shares operational
fate with the Proxy/Server itself. If the Proxy/Server goes down,
the DHCPv6 service is also disabled and the lease database must be
refreshed after the Proxy/Server reboots. Clients assign their PA
address delegations to the OMNI interface in association with the
corresponding underlay interface for each Proxy/Server.
Each AERO Proxy/Server on the OMNI link is configured to respond to
Client prefix delegation/registration requests for Provider
Independent (PI) addressing also based on the DHCPv6 service. Each
Proxy/Server is provisioned with a database of MNP-to-Client ID
mappings for all Clients enrolled in the AERO service, as well as any
information necessary to authenticate each Client. The Client
database is maintained by a central administrative authority for the
OMNI link and securely distributed to all Proxy/Servers, e.g., via
the Lightweight Directory Access Protocol (LDAP) [RFC4511], via
static configuration, etc. Clients receive the same PI service
regardless of the Proxy/Servers they select and provision their PI
prefixes for downstream-attached node addressing on ENET interfaces.
(Note: an OMNI link can instead delegate non-correlated MNPs to
Clients instead of maintaining a common synchronized database. In
that case, each Client may receive a different MNP delegation each
time it registers with the OMNI domain and may need to renumber its
downstream-attached ENETs.)
Clients associate each of their *NET underlay interfaces with FHS
Proxy/Servers. Each FHS Proxy/Server locally services one or more of
the Client's underlay interfaces, and the Client typically selects
one among them to serve as the MAP Proxy/Server (the Client may
instead select a "third-party" MAP Proxy/Server that does not
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directly service any of its underlay interfaces). All of the
Client's other FHS Proxy/Servers forward proxyed copies of RS/RA
messages between the MAP Proxy/Server and Client without assuming the
MAP role functions themselves.
Each Client typically associates with a single MAP Proxy/Server,
while all other Proxy/Servers are candidates for providing the MAP
role for other Clients. A Client can select both an FHS and MAP
Proxy/Server in a single message by including an ORH in the RS
message OAL header when it already knows the FHS and MAP addresses.
An FHS Proxy/Server assumes the MAP role when it receives an RS
message with a Destination Address that matches its own MLA, or link-
scoped All-Routers multicast. An FHS Proxy/Server assumes the proxy
role when it receives an RS message with a Destination Address that
matches the MLA of another Proxy/Server. (An FHS Proxy/Server can
also assume the proxy role when it receives an RS message addressed
to link-scoped All-Routers multicast if it can determine the SNP SRA
GUA of another Proxy/Server to serve as a MAP.)
AERO Clients and Proxy/Servers use IPv6 ND messages to maintain
adaptation layer NCEs. AERO Proxy/Servers configure their OMNI
interfaces as advertising NBMA interfaces, and therefore send unicast
RA messages with a short Router Lifetime value (e.g., ReachableTime
seconds) in response to a Client's RS message. Thereafter, Clients
send additional RS messages to keep Proxy/Server state alive.
AERO Clients and FHS/MAP Proxy/Servers include SNP ULA/GUA address
delegation (and optionally also MNP prefix delegation) DHCPv6
parameters in RS/RA messages. The IPv6 ND messages are exchanged
between the Client and any FHS Proxy/Servers acting as proxys for the
MAP Proxy/Server as specified in [I-D.templin-6man-omni3] according
to the address/prefix management schedule required by the service.
If the Client knows its MNP in advance, it can include the MNP in its
DHCPv6 prefix delegation request. If the MAP Proxy/Server accepts
the Client's MNP assertion (or if it delegates a new MNP for the
Client), it injects the MNP into the routing system and establishes
the necessary neighbor cache state.
AERO Clients and their FHS Proxy/Servers on MANETs and open INETs
must establish and maintain Identification synchronization windows in
their RS/RA exchanges. The window synchronization provides a well-
managed Identification value that the Client and Proxy/Server can use
for validating IPv6 ND messages with authentication signatures.
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All Client and Proxy/Server behaviors for the exchange of RS/RA
messages are conducted according to the Router Discovery and Prefix
Delegation specifications found in [I-D.templin-6man-omni3]. The
following sections observe all of the OMNI specifications, and
include additional specifications of the interactions of Client-
Proxy/Server RS/RA exchanges with the AERO mobility service.
4.12.2. AERO Client Behavior
AERO Clients discover the addresses of candidate FHS Proxy/Servers as
specified in the section on "Router Discovery and Prefix Delegation"
in [I-D.templin-6man-omni3]. The Client then performs RS/RA
exchanges over each of its underlay interfaces to associate with an
FHS Proxy/Server for each interface and a single MAP Proxy/Server if
necessary. The Client sends each RS (either directly via Direct
interfaces, via an IPsec tunnel for VPN interfaces, via an access
router for (M)ANET interfaces or via INET encapsulation for INET
interfaces) and waits up to RetransTimer milliseconds for an RA
message reply (see Section 4.12.3) while retrying up to
MAX_RTR_SOLICITATIONS if necessary. If the Client receives no RAs,
or if it receives an RA with Router Lifetime set to 0, the Client
SHOULD abandon attempts through the first candidate Proxy/Server and
try another Proxy/Server.
After the Client registers its underlay interfaces, it may wish to
change one or more registrations, e.g., if an interface changes
address or becomes unavailable, if traffic selectors change, etc. To
do so, the Client prepares an RS message to send over any available
underlay interface as above. The RS includes an OMNI option with
prefix registration/delegation information and with an Interface
Attributes sub-option specific to the selected underlay interface.
When the Client receives the MAP Proxy/Server's RA response, it has
assurance that both the MAP and FHS Proxy/Servers have been updated
with the new information.
If the Client wishes to discontinue use of a MAP Proxy/Server it
issues an RS message over any underlay interface with an OMNI Proxy/
Server Departure sub-option with an L3ADDR that encodes the (old) MAP
Proxy/Server's SNP SRA GUA. When the MAP Proxy/Server processes the
message, it releases any MNPs, sets the NCE state for the Client to
DEPARTED and returns an RA reply with Router Lifetime set to 0.
After a short delay (e.g., 2 seconds), the MAP Proxy/Server withdraws
the MNP from the routing system. (Alternatively, when the Client
associates with a new FHS/MAP Proxy/Server it can include an OMNI
"Proxy/Server Departure" sub-option in RS messages with an L3ADDR
that encodes the SNP SRA GUAs of the Old FHS/MAP Proxy/Servers.)
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4.12.3. AERO Proxy/Server Behavior
AERO Proxy/Servers act as both IP routers and IPv6 ND proxys, to
support address and prefix delegation services for Clients. When a
FHS/MAP Proxy/Server receives a prospective Client's secured RS
message, it SHOULD return an immediate RA reply with Router Lifetime
set to 0 if it is currently too busy or otherwise unable to service
the Client; otherwise, it processes the RS and performs DHCPv6
address delegation for SNP ULA/GUA pairs while returning the ULA/GUA
prefixes per [RFC8028] as specified in [I-D.templin-6man-omni3]. If
the RS message also contains DHCPv6 prefix delegation parameters the
FHS Proxy/Server processes the prefix delegations locally as a MAP or
forwards a proxyed version of the RS to another candidate MAP Proxy/
Server.
When the MAP Proxy/Server processes the RS, it determines the correct
MNPs for the Client by processing OMNI DHCPv6 sub-option(s). When
the MAP Proxy/Server returns the MNPs, it also creates a forwarding
table entry for each MNP resulting in BGP updates (see:
Section 4.2.3). The MAP Proxy/Server then returns an RA to the
Client via the FHS Proxy/server as specified in Section 15 of
[I-D.templin-6man-omni3].
After the initial RS/RA exchange, the MAP Proxy/Server maintains a
ReachableTime timer for each of the Client's underlay interfaces
individually (and for the Client's NCE collectively) set to expire
after ReachableTime seconds. If the Client (or an FHS Proxy/Server)
issues additional RS messages, the MAP Proxy/Server sends an RA
response and resets ReachableTime. If the MAP Proxy/Server receives
an IPv6 ND message with a prefix release indication it sets the
Client's NCE to the DEPARTED state and withdraws the MNP routes from
the routing system after a short delay (e.g., 2 seconds). If
ReachableTime expires before a new RS is received on an individual
underlay interface, the MAP Proxy/Server marks the interface as DOWN.
If ReachableTime expires before any new RS is received on any
individual underlay interface, the MAP Proxy/Server sets the NCE
state to STALE and sets a 10 second timer. If the MAP Proxy/Server
has not received a new RS or uNA message with a prefix release
indication before the 10 second timer expires, it deletes the NCE and
withdraws the MNP routes from the routing system.
The MAP Proxy/Server processes any IPv6 ND messages pertaining to the
Client while forwarding to the Client or responding on the Client's
behalf as necessary. The MAP Proxy/Server may also issue unsolicited
RA messages, e.g., with reconfigure parameters to cause the Client to
renegotiate its prefix delegation/registrations, with Router Lifetime
set to 0 if it can no longer service this Client, etc. The MAP
Proxy/Server may also receive carrier packets via the secured
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spanning tree that contain initial data sent while route optimization
is in progress. The MAP Proxy/Server reassembles the enclosed OAL
packets/fragments, then re-encapsulates/re-fragments and sends the
carrier packets to the target Client via an FHS Proxy/Server if
necessary. Finally, If the NCE is in the DEPARTED state, the old MAP
Proxy/Server forwards any OAL packets/fragments it receives from the
secured spanning tree and destined to the Client to the new MAP
Proxy/Server, then deletes the entry after DepartTime expires.
Note: Clients SHOULD arrange to notify former MAP Proxy/Servers of
their departures, but MAP Proxy/Servers are responsible for expiring
NCEs and withdrawing MNP routes even if no departure notification is
received (e.g., if the Client leaves the network unexpectedly). MAP
Proxy/Servers SHOULD therefore set Router Lifetime to ReachableTime
seconds in solicited RA messages to minimize persistent stale cache
information in the absence of Client departure notifications. A
short Router Lifetime also ensures that proactive RS/RA messaging
between Clients and FHS Proxy/Servers will keep any NAT state alive
(see above).
Note: All Proxy/Servers on an OMNI link MUST advertise consistent
values in the RA Cur Hop Limit, M and O flags, Reachable Time and
Retrans Timer fields the same as for any link, since unpredictable
behavior could result if different Proxy/Servers on the same link
advertised different values.
4.12.3.1. Additional Proxy/Server Considerations
AERO Clients register with FHS Proxy/Servers for each underlay
interface. Each of the Client's FHS Proxy/Servers in turn inform the
MAP Proxy/Server of the Client's underlay interface(s) that it
services. For Clients on Direct and VPN/IPsec underlay interfaces,
the FHS Proxy/Server for each interface is directly connected, for
Clients on (M)ANET underlay interfaces the FHS Proxy/Server is
located on the (M)ANET/INET boundary, and for Clients on INET
underlay interfaces the FHS Proxy/Server is located somewhere in the
connected Internetwork. When FHS Proxy/Server "B" processes a Client
registration, it must either assume the MAP role or forward a proxyed
registration to another Proxy/Server "A" acting as the MAP. Proxy/
Servers satisfy these requirements as follows:
* when FHS Proxy/Server "B" receives a Client RS message, it first
verifies that the OAL Identification is within the window for the
AFV associated with the NCE for this Client and authenticates the
message. If no NCE was found, Proxy/Server "B" instead creates
one in the STALE state and caches the Client-supplied Interface
Attributes, Origin Indication and Neighbor Synchronization sub-
option parameters as well as the Client's observed L2 address
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(noting that it may differ from the Origin address if there were
NATs on the path). Proxy/Server "B" then examines the RS OAL
header ORH extension. If Segments Left is greater than 0 and the
next hop ORH Address[i] contains the SNP SRA GUA of a different
Proxy/Server "A", Proxy/Server "B" prepares a separate proxyed
version of the RS message with Source Address set to the MLA of
the Client and with Destination Address set to link-scoped All-
Routers multicast. Proxy/Server "B" then sets the OAL header
Source Address to its own SNP SRA GUA and Destination Address to
Proxy/Server A's SNP SRA GUA. Proxy/Server "B" also writes its
own L2 address information over the Interface Attributes sub-
option L2 information supplied by the Client, omits or zeros the
Origin Indication sub-option then forwards the message into the
OMNI link secured spanning tree.
* when MAP Proxy/Server "A" receives the RS, it assumes the MAP
role, delegates MNPs for the Client if necessary, and creates/
updates a NCE indexed by the Client's MLA with FHS Proxy/Server
"B"'s Interface Attributes as the link layer address information
for this FHS ifIndex. MAP Proxy/Server "A" then prepares an RA
message with Source Address set to its own MLA, Destination
Address set to the Client's MLA, and with OMNI option DHCPv6 sub-
options with the prefix delegation results. MAP Proxy/Server "A"
then encapsulates the RA in an OAL header with Source Address set
to its own SNP SRA GUA, Destination Address set to the SNP SRA GUA
of FHS Proxy/Server "B" and with an ORH extension that includes
the Client's MLA. MAP Proxy/Serer "A" then finally performs
fragmentation if necessary and sends the resulting carrier packets
into the secured spanning tree.
* when FHS Proxy/Server "B" reassembles the RA, it locates the
Client NCE based on OAL addressing information. If the RA message
includes an OMNI "Proxy/Server Departure" sub-option with non-zero
old FHS/MAP Proxy/Server SNP GUAs that do not match its own GUA,
FHS Proxy/Server "B" first sends a uNA to the old FHS/MAP Proxy/
Servers named in the sub-option. Proxy/Server "B" then re-inserts
the cached Neighbor Synchronization sub-option for this Client
while updating the window synchronization parameters. Proxy/
Server "B" then resets the RA Source Address to its own MLA and
resets the RA Destination Address to the Client's MLA.
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* Proxy/Server "B" then re-encapsulates the message with OAL Source
Address set to its own MLA and OAL Destination Address set to the
Client's MLA. Proxy/Server "B" also includes an appropriate
Identification value and authentication signature if necessary,
then includes the Client's Interface Attributes sub-option and
writes the cached observed L2 addresses into an Origin Indication
sub-option. Proxy/Server "B" sets the P flag in the RA flags
field to indicate that the message has passed through a proxy
[RFC4389] then returns the RA to the Client.
* The Client repeats this process over each of its additional
underlay interfaces while treating each additional FHS Proxy/
Server "C", "D", "E", etc. as a proxy to facilitate RS/RA
exchanges between MAP "A" and the Client. The Client creates/
updates NCEs for each such FHS Proxy/Server as well as the MAP
Proxy/Server in the process.
After the initial RS/RA exchanges each FHS Proxy/Server forwards any
of the Client's carrier packets that contain OAL packets/fragments
with destinations for which there is no matching NCE to a Gateway
using OAL encapsulation with its own SNP SRA GUA as the Source
Address and with Destination Address determined by the Client. The
Proxy/Server instead forwards any OAL packets/fragments destined to a
neighbor cache target directly to the target according to the OAL or
link layer information - the process of establishing NCEs is
specified in Section 4.13.
While the Client is still associated with FHS Proxy/Servers "B", "C",
"D", "E", etc., each FHS Proxy/Server can send NS, RS and/or MI/MR/MC
messages to update the NCEs of other AERO nodes on behalf of the
Client based on changes in Interface Attributes, Traffic Selectors,
Neighbor Synchronization parameters, etc. This allows for higher-
frequency Proxy-initiated RS/RA messaging over well-connected INET
infrastructure supplemented by lower-frequency Client-initiated RS/RA
messaging over constrained (M)ANET data links.
If the MAP Proxy/Server "A" ceases to send solicited RAs, FHS Proxy/
Servers "B", "C", "D", "E", etc. can send unsolicited RAs over to the
Client with Destination Address set to (link-local) All-Nodes
multicast and with Router Lifetime set to zero to announce the MAP
Proxy/Server failure. Although Proxy/Servers "B", "C", "D", "E",
etc. can engage in IPv6 ND exchanges on behalf of the Client, the
Client can also send IPv6 ND messages on its own behalf, e.g., if it
is in a better position to convey state changes.
If the Client becomes unreachable over all underlay interfaces it
serves, the MAP Proxy/Server sets the NCE state to DEPARTED and
retains the entry for DepartTime seconds. While the state is
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DEPARTED, the MAP Proxy/Server forwards any OAL packets/fragments
destined to the Client to a new MAP Proxy/Server if known; otherwise,
it discards the OAL packets/fragments. When DepartTime expires, the
MAP Proxy/Server deletes the NCE, withdraws any MNP routes and
discards any further carrier packets that contain OAL packets/
fragments destined to the former Client.
4.12.3.2. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track MAP Proxy/Server reachability
in a fashion that parallels Bidirectional Forwarding Detection (BFD)
[RFC5880]. Each FHS Proxy/Server can then quickly detect and react
to failures so that cached information is re-established through
alternate paths. The NUD control messaging is carried only over
well-connected ground domain networks (i.e., and not low-end
aeronautical radio links) and can therefore be tuned for rapid
response.
FHS Proxy/Servers can perform continuous NS/NA(NUD) exchange with the
MAP Proxy/Server, e.g., one exchange per N seconds. The FHS Proxy/
Server sends the NUD message via the spanning tree with its own SNP
SRA GUA as the OAL Source Address and the SNP SRA GUA of the MAP
Proxy/Server as the OAL Destination Address. The MAP Proxy/Server
responds with a NUD reply. When the FHS Proxy/Server also sends RS
messages to a MAP Proxy/Server on behalf of Clients, the resulting RA
responses can be considered as equivalent hints of forward progress.
This means that the FHS Proxy/Server need not also send a periodic
NUD message if it has already sent an RS within the same period. If
the MAP Proxy/Server fails (i.e., if the FHS Proxy/Server ceases to
receive advertisements), the FHS Proxy/Server can quickly inform
Clients by sending unsolicited RA messages
The FHS Proxy/Server sends unsolicited RA messages with Source
Address set to the MAP Proxy/Server's MLA, Destination Address set to
(link-local) All-Nodes multicast, and Router Lifetime set to 0. The
FHS Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages
separated by small delays [RFC4861]. Any Clients that had been using
the failed MAP Proxy/Server will receive the RA messages and select a
different Proxy/Server to assume the MAP role.
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4.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization
AERO nodes invoke address resolution, multilink forwarding and route
optimization when they need to forward the initial original IP
packets/parcels of flows to new neighbors over (M)ANET/INET
interfaces as well as for ongoing multilink forwarding coordination
with existing neighbors.
Possible Source and Destination Addresses for original IP packets
that traverse a local (M)ANET/INET and/or the rest of the OMNI link
include addresses taken from an FNP or MNP, or the SNP GUA assigned
to a Client. The flow is then identified by the 3-tuple consisting
of the IPv6 Source Address, Destination Address and Flow Label.
Address resolution is based on an IPv6 ND NS/NA(AR) messaging
exchange between an Address Resolution Source (ARS) and the target
neighbor as the Address Resolution Target (ART). The ARS engages
address resolution by sending NS(AR) messages to determine adaptation
and link-layer address mappings for the ART network layer address.
The ARS discovers this information in any OMNI Interface Attributes
sub-options included in NA(AR) messages returned by the ART. Both
the ARS and ART can update their Destination Caches based on any peer
IPv6 addresses and/or update their routing tables based on any Route
Information Options (RIOs) [RFC4191] included in the NS/NA(AR)
exchange.
The original source or its current FHS/MAP Proxy/Server serves as the
ARS. Either the ART itself or the current LHS/MAP Proxy/Server (or
Relay) for the ART serves as the Address Resolution Responder (ARR),
i.e., the NA(AR) source.
Address resolution is initiated by the first eligible ARS closest to
the original source as follows:
* For Clients on VPN/IPsec and Direct interfaces, the Client's FHS
Proxy/Server is the ARS.
* For Clients on (M)ANET interfaces, either the FHS Proxy/Server or
the Client itself may be the ARS.
* For Clients on INET interfaces, the Client itself is the ARS.
* For FNP correspondent nodes on foreign links/networks serviced by
a Relay, the Relay is the ARS.
* For Clients that engage the MAP Proxy/Server in "mobility anchor"
mode, the MAP Proxy/Server is the ARS.
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* For peer Clients within the same (M)ANET/ENET, address resolution
and route optimization is through receipt of Redirect messages.
The AERO routing system directs an address resolution request sent by
the ARS to the ARR. The ARR then returns an address resolution reply
which must include information that is complete, current, consistent
and authentic. Both the ARS and ARR are then jointly responsible for
periodically refreshing the address resolution, and for quickly
informing each other of any changes. Following address resolution,
the ARS and ART perform subsequent multilink forwarding and route
optimization exchanges to maintain optimal forwarding profiles for
each distinct flow.
During address resolution, multilink forwarding and/or route
optimization an IPv6 ND message source may attach a small number of
original IP packets/parcels associated with the message exchange as
composite packet extensions per [I-D.templin-6man-omni3]. The
authentication signatures and/or lower-layer security features
employed at the OAL source and each OAL intermediate system will
provide authorization and integrity services for both the IPv6 ND
messages and their IP packet/parcel attachments. The final OAL
intermediate system in the path will then securely forward the IPv6
ND message IP packet/parcel attachments to the target.
The source can attach original IP packets/parcels to the subject IPv6
ND message, but this may cause the message size to exceed the IPv6
minimum MTU and/or result in sub-optimal forwarding for the IP
packet/parcel attachments. In that case, the source can instead
create small MC "pilot" messages used to transport the original IP
packets as attachments over shortest paths determined by routing.
The OAL source can attach as many IP packets/parcels as will fit
without causing the OAL packet to exceed the minimum OAL Fragment
Size (OFS) using the composite packet construct discussed in
[I-D.templin-6man-omni3].
When the target Proxy/Server or Client receives a pilot MC, it
removes all passenger attachment packets then delivers the original
IP packet(s) to the destination. This service supports assured (but
sub-optimal) short-term delivery of protocol data while neighbor
coordination is in progress without creating network state.
The address resolution, multilink forwarding and route optimization
procedures are specified in the following sections.
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4.13.1. Multilink Address Resolution
The IP layer engages address resolution over OMNI interfaces the same
as specified in Section 7 of [RFC4861] including the sending and
receiving of NS/NA(AR) messages as well as their implications for
neighbor cache entry creation and state management. The OMNI
interface therefore exhibits an IP layer behavior that is
indistinguishable from an ordinary Ethernet interface while managing
adaptation layer state at a layer below IP as discussed below.
When one or more original IP packets/parcels for a flow 3-tuple are
forwarded over an OMNI interface, the ARS checks the Destination
Cache to determine whether there is a NCE that matches the
Destination Address. If there is a NCE in the REACHABLE state, the
ARS invokes the OAL and forwards the resulting carrier packets
according to the cached state then returns from processing.
Otherwise, if there is no NCE the ARS creates one in the INCOMPLETE
state. The ARS then prepares an Address Resolution NS(AR) message to
send toward an ART. The resulting NS(AR) message must be sent
securely and includes Source, Destination and Target Addresses as
discussed in Section 4.5.1. The NS(AR) message also includes
Interface Attributes for any of the source Client's underlay
interfaces plus RIOs for any of its MNPs.
The ARS then includes an OMNI option with an Authentication sub-
option (if necessary), Interface Attributes and/or Traffic Selectors
for all of the source Client's underlay interfaces. The ARS then
calculates and includes an authentication signature (if necessary)
followed by the checksum, then submits the NS(AR) message for OAL
encapsulation.
When the ARS is a FHS Proxy/Server, it sets the OAL Source Address to
the Client's SNP GUA and sets the OAL Destination Address to the FNP/
MNP SRA GUA or SNP GUA corresponding to the ART. The ARS then
performs L2 encapsulation/fragmentation and sends the resulting
carrier packets into the SRT secured spanning tree without
decrementing the network layer TTL/Hop Limit field.
When the ARS is a Client, it must instead use its own MLA as the OAL
Source Address and the MLA of the interface-specific FHS Proxy/Server
as the OAL Destination Address. If the Client is in a MANET or an
open INET, it next calculates and includes an authentication
signature then includes an OAL IPv6 Extended Fragment Header with
Identification set to an in-window value for this FHS Proxy/Server.
The ARS Client then performs L2 encapsulation/fragmentation and
forwards the carrier packets to the FHS Proxy/Server.
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The FHS Proxy/Server then performs L2 reassembly/decapsulation,
verifies the Identification, verifies the NS(AR) checksum/
authentication signature and confirms that the Client's claimed MNP
RIO(s) and Source Address are correct. The FHS Proxy/Server then
changes the OAL Source Address to the Client's SNP GUA and changes
the OAL Destination Address to the FNP/MNP SRA GUA or SNP GUA
corresponding to the NS(AR) Target Address. The FHS Proxy/Server
next removes the IPv6 Extended Fragment Header, performs L2
encapsulation/fragmentation and sends the resulting carrier packets
into the secured spanning tree on behalf of the Client.
Note: both the source and target Client/Relay and their MAP Proxy/
Servers include current and accurate information for their multilink
Interface Attributes profile. The MAP Proxy/Servers can be trusted
to provide an authoritative ARR response and/or mobility update
message on behalf of the source/target if necessary.
Note: Address Resolution over OMNI interfaces is driven by network
layer NS/NA(AR) messaging the same as for any IP interface. The OMNI
interface rewrites the S/TLLAO with a local representation of the
address upon message reception while caching any updated information
in the adaptation layer view of the neighbor cache.
4.13.1.1. Relaying the NS(AR)
When a Gateway receives carrier packets containing the NS(AR), it
performs L2 reassembly/decapsulation and determines the next hop by
consulting its standard IPv6 forwarding table for the OAL header
Destination Address. The Gateway next decrements the OAL header Hop
Limit, performs L2 encapsulation/fragmentation and sends the carrier
packet(s) via the secured spanning tree the same as for any IPv6
router where they may traverse multiple intermediate OMNI link
segments interconnected by Gateways. The final Gateway will deliver
the carrier packets via the secured spanning tree to the LHS/MAP
Proxy/Server (or Relay) that services the ART.
4.13.1.2. NS(AR) Processing at the ARR/ART
When the LHS/MAP Proxy/Server (or Relay) of the ART receives the
NS(AR) secured carrier packets with the FNP/MNP SRA GUA or SNP GUA of
the ART as the OAL Destination Address, it performs L2 reassembly/
decapsulation then either forwards the NS(AR) to the ART or processes
it locally if it is acting as the ART's designated ARR. The LHS/MAP
Proxy/Server (or Relay) processes the message as follows:
* if the NS(AR) target matches a Client NCE in the DEPARTED state,
the (old) MAP Proxy/Server resets the OAL Destination Address to
the SNP SRA GUA of the Client's new MAP Proxy/Server. The old MAP
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Proxy/Server then decrements the OAL header Hop Limit, performs L2
encapsulation/fragmentation and forwards the resulting carrier
packets over the secured spanning tree.
* If the NS(AR) target matches a Client NCE in the REACHABLE state,
the LHS/MAP Proxy/Server (or Relay) notes whether the NS(AR)
arrived from the secured spanning tree. If the message arrived
via the secured spanning tree the LHS/MAP Proxy/Server (or Relay)
verifies the NS(AR) checksum only; otherwise, it must also verify
the message authentication signature.
* If the LHS/MAP Proxy/Server maintains a Report List for the ART,
it next records the NS(AR) Source Address in the Report List for
this ART. If the MAP Proxy/Server is the ART's designated ARR, it
forwards any original IP packet(s)/parcel(s) attached to the
NS(AR) composite packet to the ART and prepares to return an
NA(AR) as discussed below; otherwise, the LHS/MAP Proxy/Server
determines the underlay interface for the ART and proceeds as
follows:
- If the LHS/MAP Proxy/Server is also the LHS Proxy/Server on the
underlay interface used to convey the NS(AR) to the ART, it
includes an OAL IPv6 Extended Fragment Header with an in-window
Identification for the ART Client and authentication signature
if necessary then recalculates the NS(AR) checksum. The Proxy/
Server then changes the OAL Source Address to its own MLA and
OAL Destination Address to the MLA of the ART, decrements the
OAL Hop Limit, performs L2 encapsulation/fragmentation and
forwards the resulting carrier packets over the underlay
interface to the ART.
- If the MAP Proxy/Server is not the LHS Proxy/Server on the
underlay interface used to convey the NS(AR) to the ART, it
instead changes the OAL Source Address to its own SNP SRA GUA
and changes the OAL Destination Address to the SNP SRA GUA of
the LHS Proxy/Server for a selected ART interface. The MAP
Proxy/Server next decrements the OAL Hop Limit, performs L2
encapsulation/fragmentation and forwards the resulting carrier
packets over the secured spanning tree.
- When the LHS Proxy/Server receives the carrier packets, it
performs L2 reassembly/decapsulation, verifies the NS(AR)
checksum, then forwards to the ART while changing the OAL
Source and Destination Addresses to MLAs as above. The LHS
Proxy/Server also includes an IPv6 Extended Fragment Header and
authentication signature if necessary while recalculating the
checksum the same as described above.
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* If the NS(AR) target matches one of its FNP routes, the MAP/LHS
Proxy/Server serves as both a Relay and an ARR, since the Relay
forwards original IP packets/parcels toward FNP target nodes at
the network layer.
* Note: when the target's MAP Proxy/Server acts as the ARR, it
detaches any original IP packets attached to the NS(AR) and
attaches them to an MC message addressed to the ART. The MAP
Proxy/Server then forwards the resulting composite packet into the
secured spanning tree or includes an authentication signature if
the MAP is also an LHS Proxy/Server of the ART.
If the ARR is a Relay or the ART itself, it first creates or updates
a NCE for the NS(AR) MLA Source Address while caching all Interface
Attributes and Traffic Selector information in the NCE and caching
any IPv6 addresses for the original source found in the Interface
Attributes (plus the MLA) in the Destination Cache. The ARR then
installs any RIO MNP prefixes in the routing table with next hop set
to the LLA corresponding to the neighbor's MLA via the OMNI
interface. Next, the ARR prepares a solicited NA(AR) message to
return to the ARS with the IPv6 Source Address set to the ART's MLA,
with IPv6 Destination Address set to the NS(AR) Source Address, and
with Target Address set to the NS(AR) Target Address.
The ARR then includes RIOs for all of the ART's MNPs plus Interface
Attributes and Traffic Selector sub-options for all of the ART's
underlay interfaces with current information for each interface
including their SNP GUA addresses. The ARR next sets the NA(AR)
message R flag to 1 (as a router) and S flag to 1 (as a response to a
solicitation) and sets the O flag to 1 (as an authoritative
responder).
The ARR finally includes an authentication signature and IPv6
Extended Fragment Header and an ORH with addressing information for
the ARS MAP/FHS Proxy/Server if necessary. The ARR next calculates
the NA(AR) message checksum then submits the NA(AR) for encapsulation
with OAL Source Address set to its own MLA and Destination Address
set to either the MLA that appeared in the NS(AR) OAL source for
(M)ANET traversal or the NS(AR) source itself for INET traversal.
The ARR then performs L2 encapsulation/fragmentation, and forwards
the resulting carrier packets.
When the ART's FHS Proxy/Server receives carrier packets sent by an
ART acting as an ARR on its own behalf, it performs L2 reassembly and
decapsulation then verifies the OAL Identification and NA(AR) message
checksum/authentication signature. The Proxy/Server then verifies
that any RIO information is acceptable, changes the OAL Source
Address to the Client's SNP GUA and changes the OAL Destination
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Address to the Address[i] found in the ORH corresponding to the
NS(AR) Source Address. The Proxy/Server next decrements the OAL Hop
Limit, removes the OAL Extended Fragment Header, performs L2
encapsulation/fragmentation and finally forwards the resulting
carrier packets into the secured spanning tree.
4.13.1.3. Relaying the NA(AR)
When a Gateway receives NA(AR) carrier packets, it performs L2
reassembly/decapsulation and determines the next hop by consulting
its standard IPv6 forwarding table for the OAL header Destination
Address. The Gateway then decrements the OAL header Hop Limit,
performs L2 encapsulation/fragmentation and forwards the resulting
carrier packets via the SRT secured spanning tree where they may
traverse multiple intermediate OMNI link segments interconnected by
other Gateways. The final-hop Gateway will deliver the carrier
packets via the secured spanning tree to a Proxy/Server for the ARS.
4.13.1.4. ARS MAP Proxy/Server NA(AR) Processing
If the ARS Client's MAP Proxy/Server maintains a Report List, the
carrier packets containing the NA(AR) will arrive at the MAP due to
the OAL Destination Address supplied by the ART (see above). This
source MAP then performs L2 reassembly/decapsulation and records the
NA(AR) Target Address in the Report List for this source Client. The
MAP then leaves the OAL Source Address unchanged, but changes the OAL
Destination Address to the SNP GUA corresponding to the ARS. The MAP
then decrements the OAL header Hop Limit, performs L2 encapsulation/
fragmentation and sends the resulting carrier packets into the
secured spanning tree.
4.13.1.5. Processing the NA(AR) at the ARS
When the ARS receives NA(AR) carrier packets, it performs L2
reassembly/decapsulation then searches for a NCE that matches the
NA(AR) Source Address. The ARS then processes the message the same
as for standard IPv6 Address Resolution [RFC4861]. In the process,
it caches all OMNI option Interface Attributes and Traffic Selectors
in the NCE for the NA(AR) MLA Source Address and caches any IPv6
addresses for the ART found in the Interface Attributes (plus the
MLA) in the Destination Cache. The ARS then installs any RIO MNP
prefixes in the routing table with next hop set to the LLA
corresponding to the NA(AR) MLA Source Address via the OMNI
interface. All included Interface Attributes sub-options plus RIOs
together provide the address mapping information necessary to satisfy
address resolution.
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When the ARS is a Client, the SRT secured spanning tree will first
deliver the solicited NA(AR) message to the Client's FHS Proxy/
Server, which rewrites the OAL header addresses, includes an OAL
Extended Fragment Header with an in-window Identification for this
Client, and forwards the message to the Client. If the Client is on
a well-managed ANET, physical security and protected spectrum ensures
security for the NA(AR) without needing an additional authentication
signature or Identification; if the Client is in a MANET or in the
open INET the Proxy/Server must instead include an Identification and
authentication signature (while adjusting the OMNI option size, if
necessary). The Proxy/Server changes the OAL Source Address to its
own MLA and changes the OAL Destination Address to the MLA of the
Client when it forwards the NA(AR). The Proxy/Server then decrements
the OAL Hop Limit, performs L2 encapsulation/fragmentation and
forwards the resulting carrier packets over the underlay interface to
the Client.
4.13.1.6. Reliability
After the ARS transmits the first NS(AR), it should wait up to
RETRANS_TIMER seconds to receive a responsive NA(AR). The ARS can
then retransmit the NS(AR) up to MAX_UNICAST_SOLICIT times before
giving up.
4.13.2. Multilink Forwarding
Following address resolution, the ARS and ART (i.e., the end system
Clients or their respective Proxy/Servers) can assert per-flow
multilink forwarding paths through underlay interface pairs serviced
by the same Source/Destination Addresses by sending MI/MR/MC messages
with OMNI Neighbor Synchronization sub-options. The MI/MR/MC
messages establish per-flow multilink forwarding and header
compression state in OAL intermediate systems in the path between the
ARS and ART. Note that either the ARS or ART can independently
initiate multilink forwarding by sending MI messages on behalf of
specific flows over underlay interface pairs.
The source Client or FHS Proxy/Server uses the Source Address of the
original IP packet as the MI Target Address, uses its own MLA as the
MI Source Address and uses the Destination Address of the original IP
packet as the MI Destination Address. The source Client or FHS
Proxy/Server then includes the Flow Label of the original IP packet
set according to [RFC6437][RFC6438] then finally performs OAL
encapsulation while including the MLA of the target neighbor in an
ORH extension. The flow 3-tuple is then identified by the MI Target
Address, Destination Address and Flow Label.
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When the target Client or LHS Proxy/Server returns an MR, it sets the
Destination Address to the same address that appeared in the MI
Source Address, sets the Target Address to the same address that
appeared in the MI Destination Address and sets the Source Address to
its own MLA. The target Client or LHS Proxy/Server then sets the
Flow Label to the same value that appeared in the MI and finally
performs OAL encapsulation while including the MLA of the source
neighbor in an ORH extension.
When an OAL source asserts a multilink forwarding path through the
transmission of an MI message, it includes an IPv6 Minimum Path MTU
Hop-by-Hop Option for the (adaptation layer) IPv6 header per
[RFC9268]. Each OAL intermediate node along the path then updates
the minimum MTU per the specification. When the OAL destination
responds with an MR message, it returns an IPv6 Minimum Path MTU Hop-
by-Hop (HBH) option based on the one it received in the MI message
per [RFC9268]. This allows the OAL source to discover any OAL
Fragment Size (OFS) limitations for this OAL destination (see:
[I-D.templin-6man-omni3]). For this reason, OAL nodes that connect
SRT segments MUST implement [RFC9268].
The multilink forwarding profile provides support for redundant paths
that each OAL node can harness to its best advantage. For example,
OAL nodes can use traffic selectors to distribute different traffic
types over available multilink paths, while other factors such as
metrics, cost, provider, etc. can also provide useful decision
points. OAL nodes can also employ multilink forwarding for fault
tolerance by sending redundant data over multiple paths
simultaneously, or for load balancing where the individual packets of
a single traffic flow are spread across multiple independent paths.
OAL nodes that engage in multilink forwarding therefore must
incorporate a policy engine that selects both inbound and outbound
multilink paths for a given traffic profile at a given point in time.
This specification therefore provides multilink forwarding mechanisms
without mandating any specific multilink policy.
All Client, Proxy/Server and Gateway nodes that configure OMNI
interfaces and engage in multilink coordination include an additional
forwarding table termed the AERO Forwarding Information Base (AFIB)
that supports OAL packet/fragment forwarding based on original IP
packet flows over specific OMNI neighbor interface pairs. The AFIB
contains per-flow AERO Forwarding Vectors (AFVs) identified by the L2
address of the previous OAL hop plus a value known as the AFV Index
(AFVI). The AFVs cache uncompressed OAL header information to
support forwarding of packets with compressed headers as well as
previous/next-hop addressing and AFVI information. The AFVs also
cache window synchronization state (i.e., the starting sequence
number and window size) for each specific flow. Using the window
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synchronization state, simple Identification-based data origin
authentication is enabled at each OAL source, intermediate system and
target node.
Client and Proxy/Server OMNI interfaces manage end system AFIB
entries in conjunction with their internal neighbor cache, where the
NCEs link to (possibly) multiple AFVs with one per flow over a
specific FHS/LHS interface ifIndex pair. When OMNI interface peers
need to coordinate, they locate a NCE for the peer (established
through address resolution) then use the NCE as a nexus that
aggregates potentially many AVFs which cache AFVIs to support
multilink forwarding on a per-flow basis. Gateway OMNI interfaces
and the OMNI interfaces of Clients or Proxy/Servers acting as OAL
intermediate nodes manage transit AFIB entries independently of their
internal neighbor caches. These transit AFVs are indexed by the L2
address and AFVI supplied by the previous hop.
OAL source, intermediate system and target nodes create or update
AFVs/AFVIs when they process an MI/MR/MC initiation or response
message with an OMNI Neighbor Synchronization sub-option with the SYN
flag set (see: [I-D.templin-6man-omni3]). The Target Address of the
initiating MI (which is also the Destination Address of the
responsive MR) is considered to reside in the "First Hop Segment
(FHS)", while the Destination Address of the MI (which is also the
Target Address of the responsive MR) is considered to reside in the
"Last Hop Segment (LHS)".
The FHS and LHS roles are determined on a per-flow and per-interface-
pair basis. After address resolution, either peer is equally capable
of initiating multilink forwarding on behalf of a specific flow. The
peer that sends the initiating MI message with Neighbor
Synchronization for a specific pair becomes the FHS peer while the
one that returns the responsive MR becomes the LHS peer for that
(flow, interface pair) only. It is therefore commonplace that peers
may assume the FHS role for some flows while assuming the LHS role
for others, i.e., even though each peer maintains only a single NCE.
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When an OAL node sends/forwards an initiating MI or responsive MR
with a Neighbor Synchronization sub-option with the SYN flag set, it
creates or updates an AFV, caches the Identification window
information, caches the MI/MR and OAL IPv6 headers, records the
previous hop L2 address and AFVI, then generates a new next hop AFVI
or updates the lifetime of an already-established AFVI. The next hop
AFVI should be selected within the range [1 - (2**16-1)] unless all
values within that range are already in active use. Otherwise, the
AFVI must be selected within the range [2**16 - (2**32-1)] while the
value 0 indicates "AFVI unspecified". When the OAL node forwards
future OAL packets/fragments that include the previous hop L2 address
and AFVI, it can unambiguously locate the correct AFV and use the
cached information to forward to the next OAL hop.
OAL nodes cache AFVs for up to ReachableTime seconds following their
initial creation. If the node processes another MI/MR message
specific to an AFV, it updates ReachableTime to REACHABLE_TIME
seconds, i.e., the same as for NCEs. If ReachableTime expires, the
node deletes the AFV.
The following sections provide the detailed specifications of these
MI/MR/MC exchanges for all nodes along the forward and reverse paths.
4.13.2.1. FHS Client-Proxy/Server MI Forwarding
When an FHS OAL source has an original IP packet/parcel to send
toward an LHS OAL target, it first performs address resolution
resulting in the creation of a NCE for the SNP GUA of the target then
selects a source and target underlay interface pair. The FHS source
then uses its cached information for the target interface as LHS
information then prepares an MI message with a Neighbor
Synchronization sub-option while setting the MI Source, Target and
Destination Addresses as specified above.
The FHS source next creates an AFV then generates and assigns an AFVI
for the flow over this interface pair; the AFVI must be unique for
its communications to this next OAL hop. The FHS source then
includes an ORH with the AFVI plus Address[i] information for routing
purposes. The FHS source finally includes an OMNI Neighbor
Synchronization sub-option with window synchronization parameters and
prepares the MI message for transmission while also caching the
window synchronization parameters in the local AFV.
If the FHS source is the FHS Proxy/Server, it performs OAL
encapsulation while setting the OAL Source Address to the Client's
SNP GUA. The FHS Proxy/Server then performs L2 encapsulation/
fragmentation and forwards the resulting carrier packets into the
secured spanning tree which will deliver them to an FHS Gateway.
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If the FHS source is the FHS Client, it instead includes an
authentication signature and OAL Extended Fragment Header with an in-
window Identification for its FHS Proxy/Server if necessary. If FMT-
Forward and FMT-Mode are both set, the Client sets the Neighbor
Synchronization LHS ifIndex to the ifIndex of the target; otherwise,
it sets the ifIndex to 0 to allow the FHS Proxy/Server to select the
target ifIndex. The FHS Client then calculates the IPv6 ND message
checksum, performs OAL encapsulation, sets the OAL Source Address to
its own MLA and sets the OAL Destination Address to the MLA of the
FHS Proxy/Server. The FHS Client finally performs L2 encapsulation/
fragmentation and forwards the resulting carrier packets to the FHS
Proxy/Server.
If there are multiple OAL hops between the Client and FHS Proxy/
Server, the first OAL intermediate node reassembles the carrier
packets containing the MI then also verifies the checksum and
authentication signature. The OAL intermediate node then caches the
FHS/LHS Client addressing, AFVI and window synchronization
information as previous hop information in a new or existing AFV.
The OAL intermediate hop then creates a new unique AFVI to forward to
the next OAL hop, then both caches the AFVI and writes it into the
ORH, i.e., while over-writing the value supplied by the previous hop.
The OAL intermediate node then forwards to the next OAL hop toward
the FHS Proxy/Server which then performs the same functions as the
previous OAL hop.
When the FHS Proxy/Server receives the carrier packets, it performs
L2 reassembly/decapsulation, verifies the Identification, and
verifies the MI checksum and authentication signature. The FHS
Proxy/Server then creates an AFV (i.e., the same as the FHS Client
had done) while caching the FHS/LHS Client addressing, AFVI and
window synchronization information as previous hop information for
this AFV. The FHS Proxy/Server next generates a new unique AFVI to
forward to the next OAL hop, then both caches the AFVI in the AFV and
writes it into the ORH. The FHS Proxy/Server next calculates the MI
checksum then sets the OAL Source Address to the Client's SNP GUA and
OAL Destination Address to the ORH next hop Address[i]. The FHS
Proxy/Server finally decrements the OAL Hop Limit, removes the OAL
Extended Fragment Header, performs L2 encapsulation/fragmentation and
forwards the resulting carrier packets into the secured spanning
tree.
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4.13.2.2. FHS/intermediate/LHS Gateway MI Forwarding
Gateways in the spanning tree forward OAL packets/fragments not
explicitly addressed to themselves, while forwarding those that
arrived via the secured spanning tree to the next hop also via the
secured spanning tree and forwarding all others via the unsecured
spanning tree. When an FHS Gateway receives an MI packet over the
secured spanning tree, it performs L2 reassembly/decapsulation then
verifies the MI checksum. The FHS Gateway next creates an AFV based
on the previous hop Neighbor Synchronization information, i.e., the
same as the FHS Proxy/Server had done. The FHS Gateway then
generates a locally-unique AFVI for the next hop and both caches the
value in the AFV and copies it into the ORH.
The FHS Gateway then examines the SRT prefixes corresponding to both
the FHS and LHS. If the FHS Gateway has a local interface connection
to both the FHS and LHS (whether they are the same or different
segments), the FHS/LHS Gateway caches the MI Neighbor Synchronization
information in the AFV, and writes a new locally-unique AFVI for the
next hop into the AFV and ORH. The FHS Gateway then decrements the
OAL Hop Limit, performs L2 encapsulation/fragmentation and forwards
the resulting carrier packets into the secured spanning tree.
When the FHS and LHS Gateways are different, the LHS Gateway will
receive carrier packets over the secured spanning tree from the FHS
Gateway, noting there may be many intermediate Gateways in the path
between FHS and LHS which will update their transit AFVs in the same
fashion while selecting new locally-unique AFVIs for the next hop
based on Neighbor Synchronization and ORH information. The LHS
Gateway then performs L2 reassembly/decapsulation, verifies the
Identification, verifies the MI checksum then creates an AFV (i.e.,
the same as all previous hop Gateways had done) while caching the
Neighbor Synchronization information from the previous hop and
creating a new AFVI for the next hop. The LHS Gateway then
decrements the OAL Hop Limit, performs L2 encapsulation/fragmentation
and forwards the resulting carrier packets into the secured spanning
tree.
4.13.2.3. LHS Proxy/Server-Client MI/MR Processing
When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it performs L2 reassembly/decapsulation,
verifies the MI checksum then creates an AFV and caches the previous
hop Neighbor Synchronization and addressing information.
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If the MI Destination Address matches the SNP GUA of the target and
the LHS Proxy/Server is configured to respond on the target's behalf,
(i.e., if FMT-Forward is set) it next prepares to return a responsive
MR. The LHS Proxy/Server next creates or updates an NCE for the MI
Source Address (if necessary) with state set to STALE.
The LHS Proxy/Server then creates an MR while copying the Neighbor
Synchronization sub-option from the MI and including responsive
window synchronization information. The LHS Proxy/Server sets the MR
Source Address to its own MLA, sets the MR Destination Address to the
MI Target Address and sets the MR Target Address to the MI
Destination Address. The LHS Proxy/Server then encapsulates the MR
with OAL Source Address set to the MI OAL Destination Address, with
OAL Destination Address set to the MI OAL Source Address and with an
ORH extension with Address[i] information for the FHS Proxy/Server.
If the LHS Proxy/Server will set the MR message SYN flag, it also
writes a non-zero AFVI in the included ORH; otherwise, it writes the
value 0. The LHS Proxy/Server then calculates the MR checksum,
performs L2 encapsulation/fragmentation and forwards the resulting
carrier packets into the secured spanning tree.
The LHS Proxy/Server then creates a locally-unique AFVI for the
Client and both caches it in the newly-created AFV and writes it into
the ORH. If FMT-Forward is clear and FMT-Mode is set, the LHS Proxy/
Server next resets the Neighbor Synchronization FHS ifIndex to 0.
The LHS Proxy/Server next includes an authentication signature in the
MI if necessary, changes the OAL Source Address to its own MLA and
changes the OAL Destination Address to the MLA of the LHS Client.
The LHS Proxy/Server then decrements the OAL Hop Limit, includes an
OAL Extended Fragment Header with an appropriate Identification value
if necessary, performs L2 encapsulation/fragmentation and forwards
the resulting carrier packets to the LHS Client.
If there are multiple OAL hops between the LHS Proxy/Server and LHS
Client, the first OAL intermediate node reassembles the carrier
packets containing the MI then also verifies the checksum and
authentication signature. The OAL intermediate node then caches the
FHS/LHS Client addressing, AFVI and window synchronization
information as previous hop information in a new or existing AFV.
The OAL intermediate hop then creates a new unique AFVI to forward to
the next OAL hop, then both caches the AFVI and writes it into the
ORH, i.e., while over-writing the value supplied by the previous hop.
The OAL intermediate node then forwards to the next OAL hop toward
the LHS Client which then performs the same functions as the previous
OAL hop.
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When the LHS Client receives the carrier packets, it performs L2
reassembly/decapsulation, verifies the Identification, then verifies
the MI checksum/authentication signature. The LHS Client then
creates a NCE for the MI Source Address (if necessary) in the STALE
state and caches the MI Neighbor Synchronization information in a new
AFV associated with the NCE corresponding to the MI Source Address.
If the LHS Client will request reverse path state establishment, it
finally generates and assigns a locally-unique AFVI for a flow to be
forwarded to the previous hop, which it caches in the new AFV.
Otherwise, the LHS Client sets the reverse path AFVI to 0.
The LHS Client then prepares an MR using the same procedures as for
the LHS Proxy/Server above while including responsive window
synchronization information, the new AFVI in the ORH and with
Address[i] information necessary for OAL routing in the reverse path.
The LHS Client includes an authentication signature if necessary,
calculates the MR message checksum, then encapsulates the MR with OAL
Source Address set to its own MLA and OAL Destination Address set to
the MLA of the LHS Proxy/Server and with an ORH extension with
Address[i] information for the LHS/FHS Proxy/Servers. The LHS Client
finally includes an OAL Extended Fragment Header with an appropriate
Identification if necessary, performs L2 encapsulation/fragmentation
and forwards the resulting carrier packets to the LHS Proxy/Server.
If there are multiple OAL hops between the LHS Client and LHS Proxy/
Server, the first OAL intermediate node reassembles the carrier
packets containing the MR then also verifies the checksum and
authentication signature. If the MR Neighbor Synchronization sub-
option SYN flag is set, the OAL intermediate node then caches the
LHS/FHS Client addressing, AFVI and window synchronization
information as previous hop information in a new or existing AFV.
The OAL intermediate hop then creates a new unique AFVI to forward to
the next OAL hop, then both caches the AFVI and writes it into the
ORH, i.e., while over-writing the value supplied by the previous hop.
The OAL intermediate node then forwards to the next OAL hop toward
the LHS Proxy/Server which then performs the same functions as the
previous OAL hop.
4.13.2.4. Reverse Path Forwarding of the MR
When the LHS Proxy/Server receives the carrier packets, it performs
L2 reassembly/decapsulation, verifies the Identification and verifies
the MR checksum/authentication signature. The LHS Proxy/Server then
changes the OAL Source Address to the LHS Client's SNP GUA, changes
the OAL Destination Address to the FHS Client's SNP GUA (i.e., based
on ORH information provided by the LHS Client), removes the OAL
Extended Fragment Header and forwards the MR over the reverse path
toward the initiating FHS node, where it may traverse many
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intermediate Gateways.
Each Gateway along the reverse path processes the Neighbor
Synchronization information in the MR message in the same way that
the Gateways in the forward path had processed the MI. If the FHS
Proxy/Server forwards the message, it changes the OAL Destination
Address to the MLA of the FHS Client and changes the OAL Source
Address to its own MLA. The MR will eventually arrive at the
initiating FHS node as confirmation that AFV state is established in
all end and intermediate systems in the forward path.
Flow state is normally unidirectional from the source to the
destination, however the LHS node can elect bidirectional state by
setting the SYN flag in the MR Neighbor Synchronization sub-option.
In that case, the forward and reverse paths between the FHS initiator
and LHS responder may traverse different sets of intermediate nodes
but the source and destination would need some way to coordinate the
value used in the Flow Label. The initiator should then complete the
three-way handshake by returning an MC or a data packet with an in-
window Identification value to confirm that the SYN was received.
Under nominal conditions when the source and destination do not
coordinate their flow 3-tuples, if AFV state is needed in the reverse
path a separate MI/MR exchange between the LHS initiator and FHS
responder based on asynchronous packet arrivals may be needed. In
that case, the forward and reverse path flows bear no relation to one
another and will often include different flow 3-tuple information.
4.13.2.5. OAL End System Exchanges Following Synchronization
Following the initial MI/MR/MC exchange OAL end systems can begin
exchanging ordinary carrier packets for synchronized flows that
include AFVIs and with Identification values within their respective
send windows without requiring security signatures and/or secured
spanning tree traversal. OAL end and intermediate systems can also
consult their AFIBs when they receive carrier packets that contain
OAL packets/fragments with AFVIs to unambiguously locate the correct
AFV and can use the AFV state to forward OAL packets/fragments to the
next hop. OAL end systems must then perform continuous MI/MR/MC
exchanges to update window state, register new flows for optimized
multilink forwarding, confirm reachability and/or refresh AFIB cache
state in the path before ReachableTime expires.
While the OAL end systems continue to actively exchange OAL packets,
they are jointly responsible for updating cache state and per-
interface reachability before expiration. Window synchronization
state is performed on a per-flow basis and tracked in the AFVs which
are also linked to the appropriate NCE. However, the window
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synchronization exchange only confirms target Client reachability
over the specific underlay interface pair. Reachability for other
underlay interfaces that share the same NCE must be determined
individually using additional MI/MR/MC messages that include Neighbor
Synchronization information.
OAL sources can then begin including ORHs in OAL packets/fragments
with an AFVI that OAL intermediate systems can use for shortest-path
forwarding based on AFVIs instead of spanning tree OAL IPv6
addresses. OAL sources and intermediate systems can instead forward
OAL packets/fragments with OCH headers that include an AFVI since all
OAL nodes in the path up to (and sometimes including) the OAL
destination have already established AFVs.
When a Proxy/Server receives OAL packets/fragments destined to a
local SRT segment Client or forwards OAL packets/fragments received
from a local segment Client, it first locates the correct AFV. If
the OAL packet/fragment includes a secured IPv6 ND message, the
Proxy/Server uses the Client's NCE established through RS/RA
exchanges to re-encapsulate/re-fragment while sending outbound
secured carrier packets via the secured spanning tree and sending
inbound secured carrier packets while including an authentication
signature/checksum. For ordinary OAL packets/fragments, the Proxy/
Server uses the same AFV if directed by AFVI and/or OAL addressing.
Otherwise it locates an AFV established through an MI/MR/MC exchange
between the Client and the remote SRT segment peer, and forwards the
OAL packet/fragments without first reassembling/decapsulating.
When a source Client forwards OAL packets/fragments it can employ
header compression according to the AFVs established through an
MI/MR/MC exchange with a remote or local peer. When a target Client
receives carrier packets that contain OAL packets/fragments that
match a local AFV, the Client first verifies the Identification then
decompresses the headers if necessary, reassembles to obtain the OAL
packet then decapsulates and delivers the original IP packet/parcel
to the network layer.
When synchronized peer Clients in the same SRT segment with FMT-
Forward and FMT-Mode set discover each other's NATed L2ADDR
addresses, they can exchange carrier packets that contain OAL
packets/fragments directly with header compression using AFVIs
discovered as above (see: Section 4.13.6).
When the FHS Client or FHS Proxy/Server sends an MI for the purpose
of establishing multilink forwarding state, it should wait up to
RETRANS_TIMER seconds to receive a responsive MR. The FHS node can
then retransmit the MI up to MAX_UNICAST_SOLICIT times before giving
up.
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4.13.2.6. Dynamic Multilink Flow State Management
Following address resolution, either the ARS or ART acting as an OAL
source may immediately begin forwarding original IP packets for a
flow as composite packet attachments to "pilot" MC messages without
waiting for an initial MI/MR exchange. The messages will include an
authentication signature if necessary that covers the entire
composite packet including the MC pilot and all original IP packet
attachments.
Each MC message OMNI option contains a Neighbor Synchronization sub-
option with the SYN flag set to cause OAL intermediate systems in the
forward path to create or update AFIB state. The MC sets its
Source/Destination/Target Addresses and Neighbor Synchronization
flags the same as described for MI messages above. All OAL
intermediate systems in the forward path will process the MC message
the same as specified for MI messages above. If the MC includes an
IPv6 Minimum Path MTU HBH option, the OAL destination returns an MC
message with addresses the same as described for MR messages above
and with a responsive IPv6 Minimum Path MTU HBH option. Otherwise,
the OAL destination silently discards the MC without returning an
acknowledgement regardless of the Neighbor Synchronization flags.
The OAL source should continue to forward additional original IP
packets for the flow that arrive during a brief convergence interval
as secured MC composite packets, e.g., up to N composite packets
within a 1 second window. The OAL source can then begin forwarding
new IP packet arrivals for the flow via the unsecured spanning tree
while applying OAL encapsulation, fragmentation and header
compression. The OAL source can continue forwarding under the
optimistic expectation that AFIB state is securely established in the
forward path. As AFIB state becomes stale, the OAL source can resume
forwarding secured MC composite packets during a new convergence
interval to refresh/renew state as above before resuming via the
unsecured spanning tree.
The OAL source can also forward OAL-fragmented packets in this manner
by including the fragment body preceded by an OMNI Fragment Header
(OMNI-FH) immediately following the OAL-encapsulated MC message.
Each fragment MUST be no larger than the minimum OAL Fragment Size
(OFS) of 1024 octets to ensure they will transit the secured spanning
tree without encountering a size restriction. The fragment size is
determined by the MC message payload length minus the initial payload
length up to the beginning of the OMNI-FH, i.e., the fragment must
appear as the final trailing component of the composite packet.
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Fragmentation proceeds according to standard IPv6 fragmentation as
specified in [RFC8200] using a monotonically incrementing
Identification value. The OAL destination will reassemble these
fragments after authenticating the message, then remove the OAL
header and forward the resulting original IP packet to the final
destination. Note that these same fragmentation and reassembly
procedures can be applied during address resolution convergence -
see: Section 4.13.1. Further information on OMNI fragmentation and
reassembly can be found in [I-D.templin-6man-omni3].
4.13.3. Mobile Ad-hoc Network (MANET) Forwarding
Clients with OMNI interfaces configured over underlay interfaces with
indeterminant neighborhood properties may be connected to a Mobile
Ad-hoc NETwork (MANET). Each MANET may be either completely outside
of the range of any OMNI link Proxy/Servers or may require multihop
traversal between Clients acting as MANET routers to reach Proxy/
Servers that connect to the rest of the OMNI link. The former class
of MANETs must operate in isolation solely based on the unique IPv6
MLAs they configure locally. The latter class allows MANET routers
to extend infrastructure-based addressing information including MNPs
over multiple OMNI link hops as discussed in the OMNI specification.
MANET Clients configure their OMNI interfaces over one or more MANET
interfaces where multihop forwarding may be necessary. Routing
protocols suitable for use over MANET interfaces include OSPFv3
[RFC5340] with MANET Designated Router (OSPF-MDR) extensions
[RFC5614], OLSRv2 [RFC7181], AODVv2 [I-D.perkins-manet-aodvv2] and
others. Other services specific to MANET link-local and/or site-
local operations (including SMF [RFC6621], DLEP [RFC8175] and others)
are also considered in-scope. These services strive for optimal use
of available radio bandwidth and power consumption in their control
message transmissions, but efficient data plane operation is also
essential.
Clients must therefore reduce overhead through minimal encapsulation
and effective header compression whenever possible. For this reason,
when the MANET routing protocol discovers a new route the Client
configures a lesser-preferred forwarding table entry over the
corresponding MANET interface and a more-preferred forwarding table
entry over the OMNI interface. This will cause the network layer to
direct outbound packets to the OMNI interface, which can apply header
compression and underlay MANET interface selection.
Multilink Clients that connect a MANET to the rest of the OMNI link
act as regular Clients for exchanges with external INETs, but act as
Proxy/Servers over their MANET interfaces. Each such Client
therefore has at least two underlay interfaces, including both INET
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and MANET interfaces. The Client therefore services the MANET as if
it were a Proxy/server but presents itself as a Client to external
facing INETs. This class of Clients are also known as "Proxy/
Clients".
The process for a multihop Client to establish multilink forwarding
and header compression AFV state in the MANET is conducted in the
same fashion as described above and using the same MI/MR/MC or
unidirectional MC message exchanges. Each intermediate MANET node in
the path creates or updates AFV state in the same fashion as for
intermediate Gateways in the secured spanning tree except that the
MI/MR/MC messages require authentication signatures (unless
neighboring MANET nodes configure IPsec tunnels) and an
Identification that is within the window for its serving Proxy/Server
if the destination is outside of the local MANET. The MI/MR/MC
messages extend from the initiating FHS MANET Client, then across any
intermediate FHS MANET hops to the FHS Proxy/Client, then to the FHS
Proxy/Server, then across the secured SRT spanning tree to the LHS
Proxy/Server, then finally across any intermediate LHS MANET hops to
the responding LHS Client. In all other ways, the MI/MR/MC or
unidirectional MC exchanges are the same as discussed in
Section 4.13.2.
Following the MI/MR/MC exchanges, each MANET router in the forward
(and optionally also reverse) path in both the FHS and LHS MANETs
will have established AFVs containing multilink forwarding and header
compression state for the flow. The AFVs determine AFVI-based
forwarding based on the OCH header contents, and each MANET router
only forwards packets with in-window Identification values for the
flow. MANET routers maintain AFVs for up to ReachableTime seconds
unless they are refreshed by a new MI/MR/MC message. New window
synchronization exchanges must also be performed periodically to
avoid window exhaustion and/or spoofing based on predictable
Identifications.
Note: while the MANET routing protocol runs directly over the node's
MANET interfaces to discover routing information, the node configures
lesser-preferred forwarding table entries over the MANET interface
and corresponding more-preferred forwarding table entries over the
OMNI interface. This causes the network layer to forward outbound
packets via the OMNI interface which applies encapsulation,
fragmentation and/or header compression as necessary before
forwarding over the underlying MANET interface. The OMNI protocol
designator in the UDP port, IP protocol or Ethernet EtherType field
will then cause the packets to visit the OMNI interface of each
successive next-hop MANET node.
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4.13.4. Proxy/Server-to-Proxy/Server Route Optimization
When the FHS and LHS Proxy/Servers are both connected to an IPv6
underlay for the same SRT segment, they can forward MI/MR/MC
exchanges directly over the underlay without engaging SRT spanning
tree hops. This is made possible when the FHS and LHS Proxy/Servers
inject their SNPs into the underlay network routing system as well as
the SRT overlay routing system.
If the underlay is not secured, the FHS and LHS Proxy/Servers must
include an authentication signature with their MI/MR/MC messages,
which could either be the original authentication signature included
by their respective Clients or a new signature included by the Proxy/
Server itself. If the Proxy/Server that processes the MI/MR/MC
message determines that the message is authentic, it creates or
updates an AFV entry according to the multilink forwarding
parameters. This establishes both AFVI and Identification window
state to be used for future data traffic forwarding.
4.13.5. Gateway-to-Proxy/Server Route Optimization
When the LHS gateway and FHS Proxy/Server are both connected to an
IPv6 underlay for the same SRT segment, they can forward MI/MR/MC
exchanges directly over the underlay without engaging additional SRT
spanning tree hops. In this arrangement, the LHS Gateway acts the
same as the FHS Proxy/Server as discussed in Section 4.13.4 and
observes the requirement for including authentication signatures.
4.13.6. Client-to-Client Route Optimization
When the FHS/LHS Clients are both located on the same SRT segment,
Client-to-Client route optimization is possible following the
establishment of any necessary state in NATs in the path. Both
Clients will have already established state via their respective
shared segment Proxy/Servers (and possibly also any shared segment
Gateways) and can begin sending carrier packets directly via NAT
traversal while avoiding any Proxy/Server and/or Gateway hops.
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When the FHS/LHS Clients on the same SRT segment perform initial
MI/MR/MC exchanges to establish AFIB state, they first examine the
FMT-Forward and FMT-Mode settings to determine whether direct-path
forwarding is even possible for one or both Clients (direct-path
forwarding is only possible when FMT-Forward and FMT-Mode are both
set). The MI/MR/MC messages then include an Origin Indication (i.e.,
in addition to a Neighbor Synchronization sub-option) with the mapped
addresses discovered during the RS/RA exchanges with their respective
Proxy/Servers. After the AFV paths have been established, both
Clients can begin sending carrier packets via strict AFV paths while
establishing a direct path for Client-to-Client route optimization.
To establish the direct path, either Client (acting as the source)
transmits a bubble to the mapped L2 address for the target Client
which primes the local chain of NATs for reception of future carrier
packets from that L2 address (see: [RFC4380] and
[I-D.templin-6man-omni3]). The source Client then prepares an MI
message with its own MNP SRA GUA or SNP GUA as the Source Address,
with the MNP SRA GUA or SNP GUA of the target as the Destination
Address and with an OMNI option with an Interface Attributes sub-
option. The source Client then encapsulates the MI in an OAL header
with its own MLA as the Source Address, with the MLA of the Proxy/
Server as the Destination Address and with an in-window
Identification for the target. The source Client then performs L2
encapsulation/fragmentation with L2 headers addressed to its Proxy/
Server then sends the resulting carrier packets to the Proxy/Server.
When the Proxy/Server receives the carrier packets, it re-
encapsulates and sends them as unsecured carrier packets according to
AFIB state where they will eventually arrive at the target Client
which can perform L2 reassembly/decapsulation. Following reassembly,
the target Client prepares an MR message with its own MNP SRA GUA or
SNP GUA as the Source Address, with the MNP SRA GUA or SNP GUA of the
source Client as the Destination Address and with an OMNI option with
an Interface Attributes sub-option. The target Client then
encapsulates the MR in an OAL header with its own MLA as the Source
Address, with the MLA of the source Client as the Destination Address
and with an in-window Identification for the source Client. The
target Client then performs L2 encapsulation/fragmentation then
forwards the resulting carrier packets directly to the source Client.
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Following the initial MI/MR exchange, both Clients mark their
respective (source, target) underlay interface pairs as "trusted" for
no more than ReachableTime seconds. The Clients can then begin
exchanging ordinary data packets as OCH encapsulated carrier packets.
While the Clients continue to exchange packets via the direct path
avoiding all Proxy/Servers and Gateways, they should perform
additional MI/MR exchanges via their local Proxy/Servers to refresh
NCE state as well as send additional bubbles to the peer's Origin
address information if necessary to refresh NAT state.
Note: these procedures are suitable for a widely-deployed but basic
class of NATs. Procedures for advanced NAT classes are outlined in
[RFC6081], which provides mechanisms that can be employed equally for
AERO using the corresponding sub-options specified by OMNI.
Note: each communicating pair of Clients may need to maintain NAT
state for peer to peer communications via multiple underlay interface
pairs and/or multiple flows. It is therefore important that Origin
Indications are maintained with the correct peer interface and that
the NCE may cache information for multiple peer interfaces.
Note: the source and target Client exchange Origin information during
the secured MI/MR/MC multilink route optimization exchange. This
allows for subsequent MI/MR/MC exchanges to proceed using only the
Identification value as a data origin confirmation. However, Client-
to-Client peerings that require stronger security may also include
authentication signatures for mutual authentication.
4.13.7. Intra-(M)ANET/ENET Route Optimization
When a Client forwards an OAL packet (or an original IP packet/
parcel) from another Client connected to one of its downstream ENETs
to a peer within the same downstream ENET, the Client returns an IPv6
ND Redirect message to inform the source that that target can be
reached directly. The contents of the Redirect message are the same
as specified in [RFC4861], and should also include any RIOs with MNP
information corresponding to the target. These Redirect messages
update the Destination and Neighbor Caches the same as specified in
[RFC4861].
In the same fashion, when a Proxy/Server forwards an OAL packet (or
original IP packet/parcel) from a Client connected to one of its
downstream *NETs to a peer within the same downstream *NET, the
Proxy/Server returns an IPv6 ND Redirect message.
All other route optimization functions are conducted per the MI/MR/MC
messaging discussed in the previous sections.
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4.14. Neighbor Unreachability Detection (NUD)
AERO nodes perform Neighbor Unreachability Detection (NUD) per
[RFC4861] either reactively in response to persistent link layer
errors (see Section 4.11) or proactively to confirm reachability.
The NUD algorithm is based on periodic control message exchanges and
may further be seeded by IPv6 ND hints of forward progress, but care
must be taken to avoid inferring reachability based on spoofed
information. For example, IPv6 ND message exchanges that include
authentication codes and/or in-window Identifications may be
considered as acceptable hints of forward progress, while spurious
carrier packets should be ignored.
AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link
secured spanning tree (i.e. the same as described above) to test
reachability without risk of DoS attacks from nodes pretending to be
a neighbor. These NS/NA(NUD) messages use the MLAs of the parties
involved in the NUD test as Source and Destination Addresses. When
only reachability information is required without updating any other
NCE state, AERO nodes can instead perform NS/NA(NUD) exchanges
directly between neighbors without employing the secured spanning
tree as long as they include in-window Identifications and an
authentication signature/checksum.
After route optimization directs a source FHS peer to a target LHS
peer with one or more link layer addresses, either node may invoke
multilink forwarding state initialization to establish authentic
intermediate system state between specific underlay interface pairs
which also tests their reachability. Thereafter, either node acting
as the source may perform additional reachability probing through
NS(NUD) messages over the SRT secured or unsecured spanning tree, or
through NS(NUD) messages sent directly to an underlay interface of
the target itself. While testing a target underlay interface for a
given flow, the source can optionally continue to forward OAL
packets/fragments via alternate interfaces or maintain a small queue
of carrier packets until target reachability is confirmed.
NS(NUD) messages are encapsulated, fragmented and transmitted as
carrier packets the same as for ordinary original IP data packets/
parcels. The source encapsulates the NS(NUD) message the same as
described in Section 4.13.2 and includes an Interface Attributes sub-
option with ifIndex set to identify its underlay interface used for
forwarding. The source then includes an in-window Identification,
performs L2 encapsulation/fragmentation then forwards the resulting
carrier packets into the unsecured spanning tree directly to the
target if it is in the local segment.
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When the target receives the NS(NUD) carrier packets, it performs L2
reassembly/decapsulation, verifies that it has a NCE for this source
and that the Identification is in-window then performs OAL
reassembly. The target next verifies the NS(NUD) checksum/
authentication signature, then searches for Interface Attributes in
its NCE for the source that match the NS for the NA(NUD) reply. The
target then prepares the NA(NUD) with the Source and Destination
Addresses reversed, encapsulates and sets the OAL Source and
Destination Addresses, includes an Interface Attributes sub-option in
the NA(NUD) to identify the ifIndex of the underlay interface the
NS(NUD) arrived on and sets the Target Address to the same value
included in the NS(NUD). The target next sets the R flag to 1, the S
flag to 1 and the O flag to 1, then includes an in-window
Identification for the source. The node then performs L2
encapsulation/fragmentation and forwards the resulting carrier
packets into the unsecured spanning tree directly to the source if it
is in the local segment.
When the source receives the NA(NUD), it marks the target underlay
interface tested as "trusted". Note that underlay interface states
are maintained independently of the overall NCE REACHABLE state, and
that a single NCE may have multiple target underlay interfaces in
various "trusted/untrusted" states while the NCE state as a whole
remains REACHABLE.
4.15. Mobility Management and Quality of Service (QoS)
AERO is a fully Distributed Mobility Management (DMM) service in
which each Proxy/Server is responsible for only a small subset of the
Clients on the OMNI link. This is in contrast to a Centralized
Mobility Management (CMM) service where there are only one or a few
network mobility collective entities for large Client populations.
Clients coordinate with their associated FHS and MAP Proxy/Servers
via RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering relationships.
MAP Proxy/Servers provide a designated router service for their
dependent Clients, while FHS Proxy/Servers provide a proxy conduit
between the Client and both the MAP and OMNI link in general.
Clients are responsible for maintaining neighbor relationships with
their Proxy/Servers through periodic RS/RA exchanges, which also
serves to confirm neighbor reachability. When a Client's underlay
interface attributes change, the Client is responsible for updating
the MAP Proxy/Server through new RS/RA exchanges using the FHS Proxy/
Server as a first-hop conduit. The FHS Proxy/Server can also act as
a proxy to perform some IPv6 ND exchanges on the Client's behalf
without consuming bandwidth on the Client underlay interface.
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Note: when a Client's underlay interface address changes, the Client
and/or its (former) FHS Proxy/Server for this interface must
invalidate any AFVs based on the (changed) interface. Future data
packet forwarding will then trigger a new multilink forwarding MI/MR/
MC exchange to re-seed new AFVs in the path.
Mobility management considerations are specified in the following
sections.
4.15.1. Mobility Update Messaging
Mobile Clients (and/or their MAP Proxy/Servers) accommodate mobility
and/or multilink change events by sending secured uNA messages to
each active neighbor. When a node sends a uNA message to each
specific neighbor on behalf of a mobile Client, it sets the IPv6
Source Address to its own MNP SRA GUA or SNP ULA/GUA, sets the
Destination and Target Address to the neighbor's SNP ULA/GUA or one
of the mobile Client's MNP SRA GUAs. The uNA also includes an OMNI
option with OMNI Interface Attributes and Traffic Selector sub-
options for the mobile Client's underlay interfaces and includes an
authentication signature if necessary. The node next sets the uNA R
flag to 1, S flag to 0 and O flag to 1, then encapsulates the message
in an OAL header. Following OAL and L2 encapsulation/fragmentation,
the carrier packets containing the uNA message will then follow the
secured spanning tree and arrive at the specific neighbor.
As discussed in Section 7.2.6 of [RFC4861], the transmission and
reception of uNA messages is unreliable but provides a useful
optimization. In well-connected Internetworks with robust data links
uNA messages will be delivered with high probability, but in any case
the node can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs to
each neighbor to increase the likelihood that at least one will be
received. Alternatively, the node can send an MI(MM) message to
request an MR(MM) response (see: Section 4.5.1).
When the FHS/LHS Proxy/Server receives a secured uNA message prepared
as above, if the uNA Destination Address was its own SNP SRA ULA the
Proxy/Server uses the included OMNI option information to update its
NCE for the target but does not reset ReachableTime since the receipt
of a uNA message does not provide confirmation that any forward paths
to the target Client are working. If the Destination Address was the
SNP GUA of the FHS/LHS Client, the Proxy/Server instead changes the
OAL Source Address to its own SNP SRA ULA/GUA, includes an
authentication signature if necessary, and includes an in-window
Identification for this Client.
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4.15.2. Announcing Link-Layer Information Changes
When a Client needs to change its underlay Interface Attributes and/
or Traffic Selectors for one or more underlay interfaces (e.g., due
to a mobility event), the Client sends RS messages to its MAP Proxy/
Server (via first-hop FHS Proxy/Servers if necessary). Each RS
includes an OMNI option with Interface Attributes and/or Traffic
Selector sub-options for the ifIndex in question.
Note that the first FHS Proxy/Server may change due to the underlay
interface change. If the Client RS includes an OMNI Proxy/Server
Departure sub-option for the former FHS Proxy/Server, the new FHS
Proxy/Server can send a departure indication (see Section 4.15.5);
otherwise, any stale state in the former FHS Proxy/Server will simply
expire after ReachableTime expires with no effect on the MAP Proxy/
Server.
Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with
sending carrier packets containing user data in case one or more RAs
are lost. If all RAs are lost, the Client SHOULD re-associate with a
new Proxy/Server.
After performing the RS/RA exchange, the Client sends uNA messages to
all neighbors the same as described in the previous section.
4.15.3. Bringing New Links Into Service
When a Client needs to bring new underlay interfaces into service
(e.g., when it activates a new data link), it sends an RS message to
the MAP Proxy/Server via a FHS Proxy/Server for the underlay
interface (if necessary) with an OMNI option that includes an
Interface Attributes sub-option with interface parameters and with
link layer address information for the new link. The Client then
again sends uNA messages to all neighbors the same as described
above.
4.15.4. Deactivating Existing Links
When a Client needs to deactivate an existing underlay interface, it
sends an uNA message toward the MAP Proxy/Server via an FHS Proxy/
Server with an OMNI option with appropriate Interface Attributes
values for the deactivated link.
If the Client needs to send uNA messages over an underlay interface
other than the one being deactivated, it MUST include Interface
Attributes for any underlay interfaces being deactivated. The Client
then again sends uNA messages to all neighbors the same as described
above.
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Note that when a Client deactivates an underlay interface, neighbors
that receive the ensuing uNA messages need not purge all references
for the underlay interface from their NCEs. The Client may
reactivate or reuse the underlay interface and/or its ifIndex at a
later point in time, when it will send new RS messages to an FHS
Proxy/Server with fresh interface parameters to update any neighbors.
The manner in which the Client dynamically manages its local ifIndex
to interface mappings is a local decision, but should not be done in
a manner that could cause state inconsistencies in the network.
4.15.5. Moving Between Proxy/Servers
The Client performs the procedures specified in Section 4.12.2 when
it first associates with a new MAP Proxy/Server or renews its
association with an existing MAP Proxy/Server.
When a Client associates with a new MAP Proxy/Server, it sends RS
messages to register its underlay interfaces with the new MAP while
including the old MAP's GUA in the "Old MAP Proxy/Server GUA" field
of a Proxy/Server Departure OMNI sub-option. When the new MAP Proxy/
Server returns the RA message via the FHS Proxy/Server (acting as a
proxy), the FHS Proxy/Server sends an uNA to the old MAP Proxy/Server
(i.e., if the GUA is non-zero and different from its own). The uNA
has the MNP SRA GUA of the Client as the Target Address and the SNP
SRA GUA of the old MAP as the Destination Address and with an OMNI
Proxy/Server Departure sub-option as above. The FHS Proxy/Server
encapsulates the uNA in an OAL header with the SNP SRA GUA of the new
MAP as the Source Address and the SNP SRA GUA of the old MAP as the
Destination Address, then performs L2 encapsulation/fragmentation and
forwards the resulting carrier packets via the secured spanning tree.
When the old MAP Proxy/Server receives the carrier packets, it
decapsulates and reassembles if necessary to obtain the uNA then
changes the Client's NCE state to DEPARTED, resets DepartTime and
caches the new MAP Proxy/Server GUA. After a short delay (e.g., 2
seconds) the old MAP Proxy/Server withdraws the Client's MNP(s) from
the routing system. While in the DEPARTED state, the old MAP Proxy/
Server forwards any carrier packets received via the secured spanning
tree destined to the Client's MNP GUAs or SNP GUA to the new MAP
Proxy/Server's SNP GUA. When DepartTime expires, the old MAP Proxy/
Server deletes the Client's NCE.
Mobility events may also cause a Client to change to a new FHS Proxy/
Server over a specific underlay interface at any time such that a
Client RS/RA exchange over the underlay interface will engage the new
FHS Proxy/Server instead of the old. The Client can arrange to
inform the old FHS Proxy/Server of the departure by including a
Proxy/Server Departure sub-option for the "Old FHS Proxy/Server
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L3ADDR", and the new FHS Proxy/Server will issue a uNA using the same
procedures as outlined for the MAP above while using its own SNP SRA
GUA as the Source Address. This can often result in successful
delivery of carrier packets that would otherwise be lost due to the
mobility event.
Clients SHOULD NOT move rapidly between MAP Proxy/Servers in order to
avoid causing excessive oscillations in the AERO routing system.
Examples of when a Client might wish to change to a different MAP
Proxy/Server include a MAP Proxy/Server that has become unresponsive,
topological movements of significant distance, movement to a new
geographic region, movement to a new OMNI link segment, etc.
4.15.6. Accommodating Path Changes
After AFV state has been established for a flow, all OAL intermediate
systems in the forward path will have AFVs with header compression
state and (AFVI, L2ADDR) information for the next hop. However,
paths can fluctuate due to factors such as node mobility, routing
changes, network membership, etc. If an OAL intermediate system
forwarding OAL packets with OCH headers detects that the next hop in
the path has changed, it immediately reverts to sending the packets
with header compression disabled by including full OFH and IPv6
Extended Fragment Headers (plus full original IP headers) in future
packets.
If the OAL intermediate system receives an OCH1 packet with the Q bit
set and M bit clear during a path change event, it first decompresses
the original IP headers of each payload packet in the (packed) OAL
packet while retaining the packets as attachments to the (full) OAL
header. The OAL intermediate system then processes the OAL packet
further.
If an OAL packet is larger than the minimum OFS, the OAL intermediate
system applies OAL fragmentation to produce (sub-)fragments no larger
than the minimum OFS. If the original OAL packet/fragment had a
fragment ordinal value N, the OAL intermediate node writes the same
value N into each of the (sub-)fragments produced.
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The OAL intermediate node then encapsulates the OAL packet or
fragments as attachments to OAL-encapsulated MC messages (i.e., the
same as for initial packets during a multilink forwarding exchange)
but also includes an OMNI Neighbor Synchronization sub-option with
the "Path Change (PCH)" bit set (see: [I-D.templin-6man-omni3]. The
OAL intermediate node then applies an authentication signature and
includes an IPv6 Extended Fragment Header if necessary or admits the
MC-encapsulated packet/fragments into the secured spanning tree.
These (sub-)fragments (along with any other OAL fragments) will not
be further fragmented by other OAL intermediate nodes on the path and
will be reassembled by the OAL destination.
When the OAL destination begins to receive MC messages with full
headers and with the PCH bit set, it assumes that the network path
for this flow has changed and begins sending MC messages to the OAL
source. The OAL destination sends the MC messages subject to rate
limiting, and includes a Neighbor Synchronization OMNI sub-option
with both the ACK and RST flags set and with the most recent OAL
packet Identification recorded in the Acknowledgment field.
When the OAL source receives the MC messages with ACK and RST set, it
re-initiates multilink forwarding for this flow by issuing a new
MI/MR/MC or unidirectional MC exchange the same as for a new flow as
specified in Section 4.13.2. The AFV state in the former path then
simply becomes stale and is soon purged by the former OAL
intermediate nodes.
4.16. Multicast
Each Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) [RFC3810]
proxy service for its ENETs and/or hosted applications [RFC4605] and
acts as a Protocol Independent Multicast - Sparse-Mode (PIM-SM, or
simply "PIM") Designated Router (DR) [RFC7761] on the OMNI link.
Proxy/Servers act as OMNI link PIM routers for Clients on ANET, VPN/
IPsec or Direct interfaces, and Relays also act as OMNI link PIM
routers on behalf of nodes on other links/networks.
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Clients on VPN/IPsec, Direct or (M)ANET underlay interfaces for which
the *NET has deployed native multicast services forward IGMP/MLD
messages into the *NET. The IGMP/MLD messages may be further
forwarded by a first-hop *NET access router acting as an IGMP/MLD-
snooping switch [RFC4541], then ultimately delivered to a *NET (FHS)
Proxy/Server. The FHS Proxy/Server then acts as an ARS to send
NS(AR) messages to an ARR for the multicast source. Clients on *NET
underlay interfaces without native multicast services instead send
NS(AR) messages as an ARS to cause their FHS Proxy/Server to forward
the message to an ARR. When the ARR prepares an NA(AR) response, it
initiates PIM protocol messaging according to the Source-Specific
Multicast (SSM) and Any-Source Multicast (ASM) operational modes as
discussed in the following sections.
4.16.1. Source-Specific Multicast (SSM)
When an ARS "X" (i.e., either a Client or Proxy/Server) acting as PIM
router receives a Join/Prune message from a node on its downstream
interfaces containing one or more ((S)ource, (G)roup) pairs, it
updates its Multicast Routing Information Base (MRIB) accordingly.
For each S belonging to a prefix reachable via X's non-OMNI
interfaces, X then forwards the (S, G) Join/Prune to any PIM routers
on those interfaces per [RFC7761]. The same as for unicast
destinations, the 3-tuple of Source Address, Destination Address and
Flow Label identifies a flow for multicast group G.
For each S belonging to a prefix reachable via X's OMNI interface, X
sends an NS(AR) message (see: Section 4.13) into the secured spanning
tree which delivers it to ARR "Y" that services S. Y will then
return an NA(AR) that includes an OMNI option with Interface
Attributes and RIOs for S.
When X processes the NA(AR) it selects one or more underlay
interfaces for S and performs an MI/MR/MC multilink forwarding
exchange over the secured spanning tree while including a PIM Join/
Prune message for each multicast group of interest in the OMNI
option. If S is located behind any Proxys "Z"*, each Z* then updates
its MRIB accordingly and maintains the MNP SRA GUA or SNP GUA of X as
the next hop in the reverse path. Since Gateways forward messages
not addressed to themselves without examining them, this means that
the (reverse) multicast tree path is simply from each Z* (and/or S)
to X with no other multicast-aware routers in the path.
Following the initial combined Join/Prune and MI/MR/MC messaging, X
maintains a NCE for each S the same as if X was sending unicast data
traffic to S. In particular, X performs additional MI/MR/MC
exchanges to keep the NCE alive for up to t_periodic seconds
[RFC7761]. If no new Joins are received within t_periodic seconds, X
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allows the NCE to expire. Finally, if X receives any additional
Join/Prune messages for (S,G) it forwards the messages over the
secured spanning tree.
Client C that holds an MNP for source S may later depart from a first
Proxy/Server Z1 and/or connect via a new Proxy/Server Z2. In that
case, Y sends an MC message to X the same as specified for unicast
mobility in Section 4.15. When X receives the MC message, it updates
its NCE for the MLA for source S and sends new Join messages in
MI/MR/MC exchanges addressed to the new target Client underlay
interface connection for S. There is no requirement to send any
Prune messages to old Proxy/Server Z1 since source S will no longer
source any multicast data traffic via Z1. Instead, the multicast
state for (S,G) in Proxy/Server Z1 will soon expire since no new
Joins will arrive.
4.16.2. Any-Source Multicast (ASM)
When an ARS "X" acting as a PIM router receives Join/Prune messages
from a node on its downstream interfaces containing one or more (*,G)
pairs, it updates its Multicast Routing Information Base (MRIB)
accordingly. X first performs an NS/NA(AR) exchange to receive
address resolution information for Rendezvous Point (RP) "R" for each
G. X then includes a copy of each Join/Prune message in the OMNI
option of an MI/MR/MC message, then encapsulates the MI/MR/MC message
in an OAL header and sends the message into the secured spanning
tree.
For each source "S" that sends multicast traffic to group G via R,
Client S* that aggregates S (or its Proxy/Server) encapsulates the
original IP packets/parcels in PIM Register messages, includes the
PIM Register messages in the OMNI options of MC messages, performs
OAL encapsulation and fragmentation with Identification values within
the receive window for Client R* that aggregates R, then performs L2
encapsulation/fragmentation and forwards the resulting carrier
packets. Client R* may then elect to send a PIM Join to S* in the
OMNI option of a MC over the secured spanning tree. This will result
in an (S,G) tree rooted at S* with R as the next hop so that R will
begin to receive two copies of the original IP packet/parcel; one
native copy from the (S, G) tree and a second copy from the pre-
existing (*, G) tree that still uses MC PIM Register encapsulation.
R can then issue a MC PIM Register-stop message over the secured
spanning tree to suppress the Register-encapsulated stream. At some
later time, if Client S* moves to a new Proxy/Server, it resumes
sending original IP packets/parcels via MC PIM Register encapsulation
via the new Proxy/Server.
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At the same time, as multicast listeners discover individual S's for
a given G, they can initiate an (S,G) Join for each S under the same
procedures discussed in Section 4.16.1. Once the (S,G) tree is
established, the listeners can send (S, G) Prune messages to R so
that multicast original IP packets/parcels for group G sourced by S
will only be delivered via the (S, G) tree and not from the (*, G)
tree rooted at R. All mobility considerations discussed for SSM
apply.
4.16.3. Bi-Directional PIM (BIDIR-PIM)
Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate
approach to ASM that treats the Rendezvous Point (RP) as a Designated
Forwarder (DF). Further considerations for BIDIR-PIM are out of
scope.
4.17. Operation over Multiple OMNI Links
An AERO Client can connect to multiple OMNI links the same as for any
data link service. In that case, the Client maintains a distinct
OMNI interface for each link, e.g., 'omni0' for the first link,
'omni1' for the second, 'omni2' for the third, etc. Each OMNI link
would include its own distinct set of Gateways and Proxy/Servers,
thereby providing redundancy in case of failures.
Each OMNI link could utilize the same or different ANET/INET link
layer connections. The links can be distinguished at the link layer
via the SRT prefix in a similar fashion as for Virtual Local Area
Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through assignment
of distinct sets of MSPs on each link. This gives rise to the
opportunity for supporting multiple redundant networked paths (see:
Section 4.2.4).
The Client's network layer can select the outbound OMNI interface
appropriate for a given traffic profile while (in the reverse
direction) correspondent nodes must have some way of steering their
original IP packets/parcels destined to a target via the correct OMNI
link.
In a first alternative, if each OMNI link services different MSPs the
Client can receive a distinct MNP from each of the links. IP routing
will therefore assure that the correct OMNI link is used for both
outbound and inbound traffic. This can be accomplished using
existing technologies and approaches, and without requiring any
special supporting code in correspondent nodes or Gateways.
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In a second alternative, if each OMNI link services the same MSP(s)
then each link could assign a distinct "OMNI link Anycast" address
that is configured by all Gateways on the link. Correspondent nodes
can then perform Segment Routing to select the correct SRT, which
will then direct the original IP packet/parcel over multiple hops to
the target.
4.18. DNS Considerations
AERO Client MNs and INET correspondent nodes consult the Domain Name
System (DNS) the same as for any Internetworking node. When
correspondent nodes and Client MNs use different IP protocol versions
(e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain
A records for IPv4 address mappings to MNs which must then be
populated in Relay NAT64 mapping caches. In that way, an IPv4
correspondent node can send original IPv4 packets/parcels to the IPv4
address mapping of the target MN, and the Relay will translate the
IPv4 header and Destination Address into an IPv6 header and IPv6
Destination Address of the MN.
When an AERO Client registers with an AERO Proxy/Server, the Proxy/
Server can return the address(es) of DNS servers in RDNSS options
[RFC6106]. The DNS server provides the IP addresses of other MNs and
correspondent nodes in AAAA records for IPv6 or A records for IPv4.
4.19. Transition/Coexistence Considerations
OAL encapsulation ensures that dissimilar INET partitions can be
joined into a single unified OMNI link, even though the partitions
themselves may have differing protocol versions and/or incompatible
addressing plans. However, a commonality can be achieved by
incrementally distributing globally routable (i.e., native) IP
prefixes to eventually reach all nodes (both mobile and fixed) in all
OMNI link segments. This can be accomplished by incrementally
deploying AERO Gateways on each INET partition, with each Gateway
distributing its MNPs and/or discovering FNPs on its INET links.
This gives rise to the opportunity to eventually distribute native IP
addresses to all nodes, and to present a unified OMNI link view even
if the INET partitions remain in their current protocol and
addressing plans. In that way, the OMNI link can serve the dual
purpose of providing a mobility/multilink service and a transition/
coexistence service. Alternatively, if an INET partition is
transitioned to a native IP protocol version and addressing scheme
compatible with the OMNI link MNP-based addressing scheme, the
partition and OMNI link can be joined by Gateways.
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Relays that connect INETs/ENETs with dissimilar IP protocol versions
may need to employ a network address and protocol translation
function such as NAT64 [RFC6146].
4.20. Proxy/Server-Gateway Bidirectional Forwarding Detection
In environments where rapid failure recovery is essential, Proxy/
Servers and Gateways SHOULD use Bidirectional Forwarding Detection
(BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to
failures so that cached information is re-established through
alternate nodes. BFD control messaging is carried only over well-
connected ground domain networks (i.e., and not low-end radio links)
and can therefore be tuned for rapid response.
Proxy/Servers and Gateways can maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Gateway fails, BGP peers
will quickly re-establish routes through alternate paths the same as
for common BGP operational practice.
4.21. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the MN may be willing to
sacrifice a modicum of efficiency in order to have time-varying MNPs
that can be changed every so often to defeat adversarial tracking.
The DHCPv6 service offers a way for Clients that desire time-varying
MNPs to obtain short-lived prefixes (e.g., on the order of a small
number of minutes). In that case, the identity of the Client would
not be bound to the MNP but rather to a Node Identification value
(see: [I-D.templin-6man-omni3]) that can serve as a Client ID seed
for MNP prefix delegation. The Client would then be obligated to
renumber its internal networks whenever its MNP changes. This should
not present problems for Clients with automated network renumbering
services, however it can limit the durations of ongoing sessions that
would prefer to use a constant address.
5. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and was subject
to internal testing. The implementation is not planned for public
release.
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A write-from-scratch reference implementation is under active
internal development, with release version v0.1 tagged on December 9,
2024 and version v0.2 tagged on January 22, 2025. Future versions
will be made available for public release.
6. IANA Considerations
The IANA is instructed to assign three new Codes in the "ICMPv6
"Code" Fields - Type 136 - Neighbor Advertisement" registry of the
https://www.iana.org/assignments/icmpv6-parameters registry group
(registration procedure is Standards Action or IESG Approval). The
registry entries should appear as follows:
Code Message Name Reference
---- ------------- ----------
TBD1 Multilink Initiate (MI) [RFCXXXX]
TBD2 Multilink Respond (MR) [RFCXXXX]
TBD3 Multilink Control (MC) [RFCXXXX]
Figure 5: IPv6 ND Neighbor Solicitation Codes:
[RFCXXXX] above refers to this document, while [TBD1/TBD2/TBD3] may
be any available values. The values [250/251/252] are suggested to
support maximum forward compatibility for future specifications that
might define earlier values in this and/or other IPv6 ND message
tables.
The IANA assigned UDP port number "8060" for an experimental first
edition of AERO [RFC6706]. The Overlay Multilink Network Interface
(OMNI) specification [I-D.templin-6man-omni3] reclaims "8060" as the
service port for AERO/OMNI UDP/IP encapsulation, therefore this
document makes no IANA request. (Note: although [RFC6706] was not
widely implemented or deployed, it need not be obsoleted since it
uses ICMPv6 message type '0' (Reserved) which implementations of this
specification ignore.)
7. Security Considerations
AERO Gateways establish security associations with AERO Proxy/Servers
and Relays within their local OMNI link segments using secured
tunnels over underlay interfaces. The AERO Gateways of all OMNI link
segments in turn configure secured tunnels with neighboring AERO
Gateways for other OMNI link segments in a secured spanning tree
topology. Applicable security services include IPsec [RFC4301] with
IKEv2 [RFC7296], etc. (Note that secured direct point-to-point links
can also be used instead of or in addition to network layer
security.) Together, these services are responsible for assuring
connectionless integrity and data origin authentication with optional
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protection against replays for control messages that traverse the
secured spanning tree.
To prevent unauthorized local applications from congesting the
secured spanning tree, Proxy/Servers and Gateways configure local
access controls to permit only the BGP protocol service daemon to
source routing protocol control messages with the ULA assigned to the
OMNI interface as the source over the secured spanning tree. This
could be implemented as a port/address filtering configuration that
permits only TCP port 179 (as defined in the IANA "Service Names and
Port Numbers" registry) when using the ULA assigned to the OMNI
interface. To prevent malicious Clients from congesting the secured
spanning tree, Proxy/Servers should also rate-limit the secured IPv6
ND messages they process for the same (source, target) pair, e.g., by
applying IPv6 ND MAX_UNICAST_SOLICIT; MAX_NEIGHBOR_ADVERTISEMENT
limits.
To prevent spoofing, Proxy/Servers MUST silently discard without
responding to any unsecured IPv6 ND messages with OMNI sub-options
that would otherwise affect state. Also, Proxy/Servers MUST silently
discard without forwarding any original IP packets/parcels received
from one of their own Clients (whether directly or following OAL
reassembly) with a Source Address that does not match the Client's
MNP and/or a Destination Address that does match the Client's MNP.
Finally, Proxy/Servers MUST silently discard without forwarding any
carrier packets that include an OAL packet/fragment with Source and
Destination Addresses that both match the same MNP or SNP ULA/GUA.
AERO Clients that connect to secured ANETs need not apply additional
security to their IPv6 ND messages, since the messages will be
accepted and forwarded by a perimeter Proxy/Server that applies
security over its INET-facing interface to the secured spanning tree
(see above). AERO Clients that connect to MANETs or open INETs can
use network and/or transport layer security services such as VPNs
(e.g., IPsec tunnels) or can by some other means establish a secured
direct link to a Proxy/Server. When a VPN or direct link may be
impractical, however, INET Clients and Proxy/Servers SHOULD include
and verify authentication signatures for IPv6 ND messages as
specified in [I-D.templin-6man-omni3].
Templin Expires 22 September 2025 [Page 98]
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End systems SHOULD apply transport or higher layer security services
such as QUIC-TLS [RFC9000], TLS/SSL [RFC8446], DTLS [RFC6347], etc.
to provide a level of protection comparable to critical secured
Internet services. End systems that require host-based VPN services
SHOULD use network and/or transport layer security services such as
IPsec, TLS/SSL, DTLS, etc. AERO Proxy/Servers and Clients can also
provide a network-based VPN service on behalf of end systems, e.g.,
if the end system is located within a secured enclave and cannot
establish a VPN on its own behalf.
AERO Proxy/Servers and Gateways present targets for traffic
amplification Denial of Service (DoS) attacks. This concern is no
different than for widely-deployed VPN security gateways in the
Internet, where attackers could send spoofed packets to the gateways
at high data rates. This can be mitigated through the AERO/OMNI data
origin authentication procedures, as well as connecting Proxy/Servers
and Gateways over dedicated links with no connections to the Internet
and/or when connections to the Internet are only permitted through
well-managed firewalls. Traffic amplification DoS attacks can also
target an AERO Client's low data rate links. This is a concern not
only for Clients located on the open Internet but also for Clients in
secured enclaves. AERO Proxy/Servers and Proxys can institute rate
limits that protect Clients from receiving carrier packet floods that
could DoS low data rate links.
AERO Relays must implement ingress filtering to avoid a spoofing
attack in which spurious messages with ULA addresses are injected
into an OMNI link from an outside attacker. AERO Clients MUST ensure
that their connectivity is not used by unauthorized nodes on their
ENETs to gain access to a protected network, i.e., AERO Clients that
act as routers MUST NOT provide routing services for unauthorized
nodes. (This concern is no different than for ordinary hosts that
receive an IP address delegation but then "share" the address with
other nodes via some form of Internet connection sharing such as
tethering.)
The AERO service for MANET and open INET Clients depends on a public
key distribution service in which Client public keys and identities
are maintained in a shared database accessible to Proxy/Servers and
potential correspondent peer nodes. Similarly, each Client must be
able to determine the public key of each Proxy/Server, e.g. by
consulting an online database.
The PRL contains only public information, but MUST be well-managed
and secured from unauthorized tampering. The PRL can be conveyed to
the Client in a similar fashion as in [RFC5214] (e.g., through data
link layer login messaging, secure upload of a static file, DNS
lookups, etc.).
Templin Expires 22 September 2025 [Page 99]
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Security considerations for IPv6 fragmentation and reassembly are
discussed in [I-D.templin-6man-omni3]. In environments where
spoofing is considered a threat, all OAL nodes SHOULD employ
Identification window synchronization and OAL end systems SHOULD
configure an (end-system-based) firewall.
Security considerations for accepting link layer ICMP messages and
reflected carrier packets are discussed throughout the document.
8. Acknowledgements
Discussions in the IETF, aviation standards communities and private
exchanges helped shape some of the concepts in this work.
Individuals who contributed insights include Mikael Abrahamsson,
Felipe Magno de Almeida, Mark Andrews, Fred Baker, Amanda Baber, Bob
Braden, Stewart Bryant, Scott Burleigh, Brian Carpenter, Wojciech
Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, Sri
Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom
Herbert, Bob Hinden, Sascha Hlusiak, Lee Howard, Christian Huitema,
Zdenek Jaron, Andre Kostur, Hubert Kuenig, Eliot Lear, Ted Lemon,
Andy Malis, Satoru Matsushima, Tomek Mrugalski, Thomas Narten, Madhu
Niraula, Alexandru Petrescu, Behcet Saikaya, Michal Skorepa, Dave
Thaler, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd
Wood and James Woodyatt. Members of the IESG also provided valuable
input during their review process that greatly improved the document.
Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman
for their shepherding guidance during the publication of the AERO
first edition.
This work has further been encouraged and supported by Boeing
colleagues including Akash Agarwal, Kyle Bae, M. Wayne Benson, Dave
Bernhardt, Cam Brodie, John Bush, Balaguruna Chidambaram, Irene Chin,
Bruce Cornish, Claudiu Danilov, Sean Dickson, Don Dillenburg, Joe
Dudkowski, Wen Fang, Samad Farooqui, Anthony Gregory, Jeff Holland,
Seth Jahne, Brian Jaury, Greg Kimberly, Ed King, Madhuri Madhava
Badgandi, Laurel Matthew, Gene MacLean III, Kyle Mikos, Rob
Muszkiewicz, Sean O'Sullivan, Satish Raghavendran, Vijay Rajagopalan,
Kristina Ross, Greg Saccone, Ron Sackman, Bhargava Raman Sai Prakash,
Rod Santiago, Madhanmohan Savadamuthu, Kent Shuey, Brian Skeen, Mike
Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia Wilson,
Julie Wulff, Yueli Yang, Eric Yeh and other members of the Boeing
mobility, networking and autonomy teams. Akash Agarwal, Kyle Bae,
Wayne Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan,
Bhargava Raman Sai Prakash, Katie Tran and Eric Yeh are especially
acknowledged for their work on the AERO implementation. Chuck
Klabunde is honored for his support and guidance, and we mourn his
untimely loss.
Templin Expires 22 September 2025 [Page 100]
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This work was inspired by the support and encouragement of countless
outstanding colleagues, managers and program directors over the span
of many decades. Beginning in the late 1980s,' the Digital Equipment
Corporation (DEC) Ultrix Engineering and DECnet Architects groups
identified early issues with fragmentation and bridging links with
diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia
at UC Berkeley and the DEC Western Research Lab in Palo Alto included
investigations into large-scale networked filesystems, ATM vs
Internet and network security proxys. In the mid-1990s to early
2000s employment at the NASA Ames Research Center (Sterling Software)
and SRI International supported early investigations of IPv6, ONR UAV
Communications and the IETF. An employment at Nokia where important
IETF documents were published gave way to a present-day engagement
with The Boeing Company. The work matured at Boeing through major
programs including Future Combat Systems, Advanced Airplane Program,
DTN for the International Space Station, Mobility Vision Lab, CAST,
Caravan, Airplane Internet of Things, the NASA UAS/CNS program, the
FAA/ICAO ATN/IPS program and many others. An attempt to name all who
gave support and encouragement would double the current document size
and result in many unintentional omissions - but to all a humble
thanks.
Earlier works on NBMA tunneling approaches are found in
[RFC2529][RFC5214][RFC5569].
Many of the constructs presented in this second edition of AERO are
based on the author's earlier works, including:
* Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214]
* The Subnetwork Encapsulation and Adaptation Layer (SEAL) [RFC5320]
* Virtual Enterprise Traversal (VET) [RFC5558]
* Routing and Addressing in Networks with Global Enterprise
Recursion (RANGER) [RFC5720][RFC6139]
* The Internet Routing Overlay Network (IRON) [RFC6179]
* AERO, First Edition [RFC6706]
Note that these works cite numerous earlier efforts that are not
included here due to space limitations. The authors of those earlier
works are acknowledged for their insights.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
Templin Expires 22 September 2025 [Page 101]
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This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Commercial Airplanes (BCA)
Airplane Internet of Things (AIoT) and autonomy programs.
This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.
This work is aligned with the Boeing/Virginia Tech Network Security
Institute (VTNSI) 5G MANET research program.
Honoring life, liberty and the pursuit of happiness.
9. References
9.1. Normative References
[I-D.ietf-dhc-rfc8415bis]
Mrugalski, T., Volz, B., Richardson, M. C., Jiang, S., and
T. Winters, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", Work in Progress, Internet-Draft, draft-ietf-
dhc-rfc8415bis-08, 3 March 2025,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-dhc-rfc8415bis/>.
[I-D.templin-6man-omni3]
Templin, F. L., "Transmission of IP Packets over Overlay
Multilink Network (OMNI) Interfaces", Work in Progress,
Internet-Draft, draft-templin-6man-omni3-40, 15 March
2025, <https://datatracker.ietf.org/api/v1/doc/document/
draft-templin-6man-omni3/>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>.
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[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC9268] Hinden, R. and G. Fairhurst, "IPv6 Minimum Path MTU Hop-
by-Hop Option", RFC 9268, DOI 10.17487/RFC9268, August
2022, <https://www.rfc-editor.org/info/rfc9268>.
9.2. Informative References
[BGP] Huston, G., "BGP in 2015, http://potaroo.net", January
2016.
[CERF] Cerf, V., "The Catenet Model For Internetworking, IETF
IEN48, http://www.postel.org/ien/pdf/ien048.pdf", July
1978.
[EUI] "IEEE Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID, https://standards.ieee.org/wp-
content/uploads/import/documents/tutorials/eui.pdf", 3
August 2017.
[I-D.ietf-6man-rfc6724-update]
Buraglio, N., Chown, T., and J. Duncan, "Prioritizing
known-local IPv6 ULAs through address selection policy",
Work in Progress, Internet-Draft, draft-ietf-6man-rfc6724-
update-17, 27 January 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-
rfc6724-update-17>.
[I-D.ietf-intarea-tunnels]
Touch, J. D. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-14, 3 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
tunnels-14>.
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[I-D.ietf-rtgwg-atn-bgp]
Templin, F., Saccone, G., Dawra, G., Lindem, A., and V.
Moreno, "A Simple BGP-based Mobile Routing System for the
Aeronautical Telecommunications Network", Work in
Progress, Internet-Draft, draft-ietf-rtgwg-atn-bgp-27, 23
September 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-rtgwg-atn-bgp-27>.
[I-D.perkins-manet-aodvv2]
Perkins, C. E., Dowdell, J., Steenbrink, L., and V.
Pritchard, "Ad Hoc On-demand Distance Vector Version 2
(AODVv2) Routing", Work in Progress, Internet-Draft,
draft-perkins-manet-aodvv2-05, 22 November 2024,
<https://datatracker.ietf.org/doc/html/draft-perkins-
manet-aodvv2-05>.
[I-D.templin-6man-mla]
Templin, F., "IPv6 Addresses for Ad Hoc Networks", Work in
Progress, Internet-Draft, draft-templin-6man-mla-25, 24
September 2024, <https://datatracker.ietf.org/doc/html/
draft-templin-6man-mla-25>.
[I-D.templin-6man-parcels2]
Templin, F., "IPv6 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-6man-
parcels2-21, 2 January 2025,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
parcels2-21>.
[I-D.templin-intarea-parcels2]
Templin, F., "IPv4 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-intarea-
parcels2-15, 31 December 2024,
<https://datatracker.ietf.org/doc/html/draft-templin-
intarea-parcels2-15>.
[KAHN] Perry, T., "The Great Interconnector, IEEE Spectrum,
https://spectrum.ieee.org/bob-kahn-2667754905", May 2024.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
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[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/info/rfc1812>.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529,
DOI 10.17487/RFC2529, March 1999,
<https://www.rfc-editor.org/info/rfc2529>.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
2001, <https://www.rfc-editor.org/info/rfc3056>.
[RFC3724] Kempf, J., Ed., Austein, R., Ed., and IAB, "The Rise of
the Middle and the Future of End-to-End: Reflections on
the Evolution of the Internet Architecture", RFC 3724,
DOI 10.17487/RFC3724, March 2004,
<https://www.rfc-editor.org/info/rfc3724>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
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[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access
Protocol (LDAP): The Protocol", RFC 4511,
DOI 10.17487/RFC4511, June 2006,
<https://www.rfc-editor.org/info/rfc4511>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605,
August 2006, <https://www.rfc-editor.org/info/rfc4605>.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
<https://www.rfc-editor.org/info/rfc5015>.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
DOI 10.17487/RFC5214, March 2008,
<https://www.rfc-editor.org/info/rfc5214>.
[RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and
Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320,
February 2010, <https://www.rfc-editor.org/info/rfc5320>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
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[RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility
Route Optimization Requirements for Operational Use in
Aeronautics and Space Exploration Mobile Networks",
RFC 5522, DOI 10.17487/RFC5522, October 2009,
<https://www.rfc-editor.org/info/rfc5522>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569,
January 2010, <https://www.rfc-editor.org/info/rfc5569>.
[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET)
Extension of OSPF Using Connected Dominating Set (CDS)
Flooding", RFC 5614, DOI 10.17487/RFC5614, August 2009,
<https://www.rfc-editor.org/info/rfc5614>.
[RFC5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
DOI 10.17487/RFC5720, February 2010,
<https://www.rfc-editor.org/info/rfc5720>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 6106, DOI 10.17487/RFC6106, November 2010,
<https://www.rfc-editor.org/info/rfc6106>.
[RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin,
Ed., "Routing and Addressing in Networks with Global
Enterprise Recursion (RANGER) Scenarios", RFC 6139,
DOI 10.17487/RFC6139, February 2011,
<https://www.rfc-editor.org/info/rfc6139>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
<https://www.rfc-editor.org/info/rfc6145>.
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[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
[RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network
(IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011,
<https://www.rfc-editor.org/info/rfc6179>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<https://www.rfc-editor.org/info/rfc6296>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6621] Macker, J., Ed., "Simplified Multicast Forwarding",
RFC 6621, DOI 10.17487/RFC6621, May 2012,
<https://www.rfc-editor.org/info/rfc6621>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2",
RFC 7181, DOI 10.17487/RFC7181, April 2014,
<https://www.rfc-editor.org/info/rfc7181>.
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[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J.
Korhonen, "Requirements for Distributed Mobility
Management", RFC 7333, DOI 10.17487/RFC7333, August 2014,
<https://www.rfc-editor.org/info/rfc7333>.
[RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
Routable Cryptographic Hash Identifiers Version 2
(ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
2014, <https://www.rfc-editor.org/info/rfc7343>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8175] Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
DOI 10.17487/RFC8175, June 2017,
<https://www.rfc-editor.org/info/rfc8175>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
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[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/info/rfc9002>.
[RFC9365] Jeong, J., Ed., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
RFC 9365, DOI 10.17487/RFC9365, March 2023,
<https://www.rfc-editor.org/info/rfc9365>.
[RFC9374] Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"DRIP Entity Tag (DET) for Unmanned Aircraft System Remote
ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023,
<https://www.rfc-editor.org/info/rfc9374>.
[RFC9631] Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L.
Jalil, "The IPv6 Compact Routing Header (CRH)", RFC 9631,
DOI 10.17487/RFC9631, August 2024,
<https://www.rfc-editor.org/info/rfc9631>.
Appendix A. Non-Normative Considerations
AERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:
A.1. Implementation Strategies for Route Optimization
Address resolution and route optimization as discussed in
Section 4.13 results in the creation of NCEs. The NCE state is set
to REACHABLE for at most ReachableTime seconds. In order to refresh
the NCE lifetime before the ReachableTime timer expires, the
specification requires implementations to issue a new NS/NA(AR)
exchange to reset ReachableTime while data messages are still
flowing. However, the decision of when to initiate a new NS/NA(AR)
exchange and to perpetuate the process is left as an implementation
detail.
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One possible strategy may be to monitor the NCE watching for data
messages for (ReachableTime - 5) seconds. If any data messages have
been sent to the neighbor within this timeframe, then send an NS(AR)
to receive a new NA(AR). If no data messages have been sent, wait
for 5 additional seconds and send an immediate NS(AR) if any data
packets are sent within this "expiration pending" 5 second window.
If no additional data messages are sent within the 5 second window,
reset the NCE state to STALE.
The monitoring of the neighbor data traffic therefore becomes an
ongoing process during the NCE lifetime. If the NCE expires, future
data messages will trigger a new NS/NA(AR) exchange while the
messages themselves may be delivered over longer paths until route
optimization state is re-established.
A.2. Implicit Mobility Management
OMNI interface neighbors MAY provide a configuration option that
allows them to perform implicit mobility management in which no IPv6
ND messaging is used. In that case, the Client only transmits
carrier packets over a single interface at a time, and the neighbor
always observes carrier packets arriving from the Client from the
same L2 Source Address.
If the Client's underlay interface address changes (either due to a
readdressing of the original interface or switching to a new
interface) the neighbor immediately updates the NCE for the Client
and begins accepting and sending carrier packets according to the
Client's new address. This implicit mobility method applies to use
cases such as cellphones with both WiFi and Cellular interfaces where
only one of the interfaces is active at a given time, and the Client
automatically switches over to the backup interface if the primary
interface fails.
A.3. Direct Underlying Interfaces
When a Client's OMNI interface is configured over a Direct interface,
the neighbor at the other end of the Direct link can receive original
IP packets/parcels without any encapsulation. In that case, the
Client sends packets/parcels over the Direct link according to
traffic selectors. If the Direct interface is selected, then the
Client's packets/parcels are transmitted directly to the peer without
traversing an ANET/INET. If other interfaces are selected, then the
Client's packets/parcels are transmitted via a different interface,
which may result in the inclusion of Proxy/Servers and Gateways in
the communications path. Direct interfaces must be tested
periodically for reachability, e.g., via NUD.
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A.4. AERO Critical Infrastructure Considerations
AERO Gateways can be either Commercial off-the Shelf (COTS) standard
IP routers or virtual machines in the cloud. Gateways must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Gateways of other INETs via inter-
domain peerings. Cost for purchasing, configuring and managing
Gateways is nominal even for very large OMNI links.
AERO INET Proxy/Servers can be standard dedicated server platforms,
but most often will be deployed as virtual machines in the cloud.
The only requirements for INET Proxy/Servers are that they can run
the AERO/OMNI code and have at least one network interface connection
to the INET. INET Proxy/Servers must be provisioned, supported and
managed by the INET administrative authority. Cost for purchasing,
configuring and managing cloud Proxy/Servers is nominal especially
for virtual machines.
AERO ANET Proxy/Servers are most often standard dedicated server
platforms with one underlay interface connected to the ANET and a
second interface connected to an INET. As with INET Proxy/Servers,
the only requirements are that they can run the AERO/OMNI code and
have at least one interface connection to the INET. ANET Proxy/
Servers must be provisioned, supported and managed by the ANET
administrative authority. Cost for purchasing, configuring and
managing Proxys is nominal, and borne by the ANET administrative
authority.
AERO Relays are simply Proxy/Servers connected to INETs and/or ENETs
that provide forwarding services for non-MNP destinations. The Relay
connects to the OMNI link and engages in eBGP peering with one or
more Gateways as a stub AS. The Relay then injects its MNPs and/or
non-MNP prefixes into the BGP routing system, and provisions the
prefixes to its downstream-attached networks. The Relay can perform
ARS/ARR services the same as for any Proxy/Server, and can route
between the MNP and non-MNP address spaces.
A.5. AERO Server Failure Implications
AERO Proxy/Servers do not present a single point of failure in the
architecture since all Proxy/Servers on the link provide identical
services and loss of a Proxy/Server does not imply immediate and/or
comprehensive communication failures. Proxy/Server failure can be
quickly detected and conveyed by Bidirectional Forward Detection
(BFD) and/or proactive NUD allowing Clients to migrate to new Proxy/
Servers.
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If a Proxy/Server fails, peer carrier packet forwarding to Clients
will continue by virtue of the NCEs that have already been
established through address resolution and route optimization. If a
Client also experiences mobility events at roughly the same time the
Proxy/Server fails, uNA messages may be lost but NCEs in the DEPARTED
state will ensure that carrier packet forwarding to the Client's new
locations will continue for up to DepartTime seconds.
If a Client is left without a Proxy/Server for a considerable length
of time (e.g., greater than ReachableTime seconds) then existing NCEs
will eventually expire and both ongoing and new communications will
fail. The original source will continue to retransmit until the
Client has established a new Proxy/Server relationship, after which
time communications can continue .
Therefore, links that provide many Proxy/Servers with high
availability profiles are responsive to loss of individual
infrastructure elements, since Clients can quickly establish new
Proxy/Server relationships in event of failures.
A.6. AERO Client / Server Architecture
The AERO architectural model is client / server in the control plane,
with route optimization in the data plane. The same as for common
Internet services, the AERO Client discovers the addresses of AERO
Proxy/Servers and connects to one or more of them. The AERO service
is analogous to common Internet services such as google.com,
yahoo.com, cnn.com, etc. However, there is only one AERO service for
the link and all Proxy/Servers provide identical services.
Common Internet services provide differing strategies for advertising
server addresses to clients. The strategy is conveyed through the
DNS resource records returned in response to name resolution queries.
As of January 2020 Internet-based 'nslookup' services were used to
determine the following:
* When a client resolves the domainname "google.com", the DNS always
returns one A record (i.e., an IPv4 address) and one AAAA record
(i.e., an IPv6 address). The client receives the same addresses
each time it resolves the domainname via the same DNS resolver,
but may receive different addresses when it resolves the
domainname via different DNS resolvers. But, in each case,
exactly one A and one AAAA record are returned.
* When a client resolves the domainname "ietf.org", the DNS always
returns one A record and one AAAA record with the same addresses
regardless of which DNS resolver is used.
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* When a client resolves the domainname "yahoo.com", the DNS always
returns a list of 4 A records and 4 AAAA records. Each time the
client resolves the domainname via the same DNS resolver, the same
list of addresses are returned but in randomized order (i.e.,
consistent with a DNS round-robin strategy). But, interestingly,
the same addresses are returned (albeit in randomized order) when
the domainname is resolved via different DNS resolvers.
* When a client resolves the domainname "amazon.com", the DNS always
returns a list of 3 A records and no AAAA records. As with
"yahoo.com", the same three A records are returned from any
worldwide Internet connection point in randomized order.
The above example strategies show differing approaches to Internet
resilience and service distribution offered by major Internet
services. The Google approach exposes only a single IPv4 and a
single IPv6 address to clients. Clients can then select whichever IP
protocol version offers the best response, but will always use the
same IP address according to the current Internet connection point.
This means that the IP address offered by the network must lead to a
highly-available server and/or service distribution point. In other
words, resilience is predicated on high availability within the
network and with no client-initiated failovers expected (i.e., it is
all-or-nothing from the client's perspective). However, Google does
provide for worldwide distributed service distribution by virtue of
the fact that each Internet connection point responds with a
different IPv6 and IPv4 address. The IETF approach is like google
(all-or-nothing from the client's perspective), but provides only a
single IPv4 or IPv6 address on a worldwide basis. This means that
the addresses must be made highly-available at the network level with
no client failover possibility, and if there is any worldwide service
distribution it would need to be conducted by a network element that
is reached via the IP address acting as a service distribution point.
In contrast to the Google and IETF philosophies, Yahoo and Amazon
both provide clients with a (short) list of IP addresses with Yahoo
providing both IP protocol versions and Amazon as IPv4-only. The
order of the list is randomized with each name service query
response, with the effect of round-robin load balancing for service
distribution. With a short list of addresses, there is still
expectation that the network will implement high availability for
each address but in case any single address fails the client can
switch over to using a different address. The balance then becomes
one of function in the network vs function in the end system.
The same implications observed for common highly-available services
in the Internet apply also to the AERO client/server architecture.
When an AERO Client connects to one or more ANETs, it discovers one
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or more AERO Proxy/Server addresses through the mechanisms discussed
in earlier sections. Each Proxy/Server address presumably leads to a
fault-tolerant clustering arrangement such as supported by Linux-HA,
Extended Virtual Synchrony or Paxos. Such an arrangement has
precedence in common Internet service deployments in lightweight
virtual machines without requiring expensive hardware deployment.
Similarly, common Internet service deployments set service IP
addresses on service distribution points that may relay requests to
many different servers.
For AERO, the expectation is that a combination of the Google/IETF
and Yahoo/Amazon philosophies would be employed. The AERO Client
connects to different ANET access points and can receive 1-2 Proxy/
Server ULAs at each point. It then selects one AERO Proxy/Server
address, and engages in RS/RA exchanges with the same Proxy/Server
from all ANET connections. The Client remains with this Proxy/Server
unless or until the Proxy/Server fails, in which case it can switch
over to an alternate Proxy/Server. The Client can likewise switch
over to a different Proxy/Server at any time if there is some reason
for it to do so. So, the AERO expectation is for a balance of
function in the network and end system, with fault tolerance and
resilience at both levels.
Appendix B. Change Log
<< RFC Editor - remove prior to publication >>
Differences from earlier versions:
Draft -35 to -36
* Discussion of DHCPv6 service model for OMNI links.
Draft -34 to -35
* Further clarification on unidirectional nature of flows.
* Introduced "Proxy/Client" archetype.
Draft -33 to -34
* Significant re-work of addressing architecture to de-emphasize
CGAs and bring MLAs and ULAs/GUAs into focus.
* Clarified interactions with Destination Cache.
* Support dynamic flow state management with control messages in
the forward direction only and without waiting for an
acknowledgement.
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* Rewrite of IANA considerations to more accurately represent
registry and registry group names.
Draft -32 to -33
* Further clarifications on ORH implications plus interactions
with NS/NA message addressing.
Draft -30 to -32
* Removed Host node type. OMNI Clients can now provide
recursively-nested Proxy services for other Clients.
* Introduced notion of "transit" OAL intermediate systems as well
as DSCP markings transit systems can use to intercept control
messages.
Draft -28 to -30
* Minor MLA addressing corrections.
Draft -27 to -28
* Support for SEND/CGA per [RFC3971][RFC3972].
Draft -26 to -27
* New Code values for IPv6 NS messages to create new ND message
types for use at the adaptation layer Neighbor (Multilink)
Initiate (NI), Neighbor (Multilink) Respond (NR), Neighbor
(Multilink) Confirm (NC)).
* Changed uNA to NC (or NI/NR) globally for mobility management
and error message transport.
* IANA considerations requests message codes for NI/NR/NC.
Draft -25 to -26
* New Code values for IPv6 NS messages to create new ND message
types for use at the adaptation layer (Multilink Initiate (MI),
Multilink Respond (MR), Multilink Confirm (MC)).
* Removed ORH from responsive MR messages since those messages
now include both the PA and PI addresses of the FHS Client.
Draft -24 to -25
* Permit OAL fragmentation over secured spanning tree.
Draft -23 to -24
* No longer require ARS to steer the NS(AR) through the FHS MAP
Proxy/Server. Instead, allow the responsive NA(AR) to
naturally flow through the FHS MAP which can then update its
report list.
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* Now support asynchronous multilink forwarding, where uNA(MF)
messages are used as "pilots" to ferry original IP packets over
the secured spanning tree until MF state is established in the
unsecured spanning tree.
Draft -22 to -23
* ORH no longer necessary for NS messages, since target address
is available. ORH now only necessary for NA(MF) messages or
for any ordinary data packets sent to an MNP address and with
full headers.
* Clarifications on LLA usage.
Draft -21 to -22
* Update references.
Draft -20 to -21
* Updated IANA considerations based on IANA early review input.
* Clarifications on address resolution and multilink forwarding.
* Corrected references to "OMNI option".
Draft -19 to -20
* Clarifications on address mapping.
* "super-packet" renamed as "composite packet".
Draft -18 to -19
* S/TLLAO and MLA/LLA address mapping specified.
* LLA usage in OMNI interface IPv6 ND messages now functions
exactly as specified in [RFC4861].
Draft -17 to -18
* MLAs now locally specified, with informative reference only.
Draft -16 to -17
* Link-Local Address mapping for OMNI interfaces explained.
Draft -15 to -16
* Changed to make S/TLLAO and OMNI option mutually exclusive.
When the network layer prepares an IPv6 ND message it includes
only an S/TLLAO and no OMNI option. When the adaptation layer
prepares or forwards an IPv6 ND message, it includes only an
OMNI option and no S/TLLAO.
Draft -14 to -15
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* Introduced virtual Ethernet model for driving OMNI interface
from IP layer IPv6 ND messaging. This allows the IP layer to
interact with the OMNI interface as an ordinary IP interface
instead of an embedded virtual router.
Draft -13 to -14
* Clarified roles of OMNI interface Destination/Neighbor caches.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: fltemplin@acm.org
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