MPLS Working Group J. Rajamanickam, Ed.
Internet-Draft R. Gandhi, Ed.
Intended status: Standards Track Cisco Systems, Inc.
Expires: 21 September 2025 R. Zigler
Broadcom
T. Li
Juniper Networks
J. Dong
Huawei Technologies
20 March 2025
Post-Stack MPLS Network Action (MNA) Solution
draft-jags-mpls-ps-mna-hdr-05
Abstract
This document defines the Post-Stack MPLS Network Action (MNA)
solution for carrying Network Actions and Ancillary Data after the
MPLS label stack, based on the In-Stack MNA solution defined in "MPLS
Network Action (MNA) Sub-Stack Solution." MPLS Network Actions can
be used to influence packet forwarding decisions, carry additional
Operations, Administration, and Maintenance (OAM) information in the
MPLS packet, or perform user-defined operations. This solution
document addresses the Post-Stack network action and Post-Stack data
specific requirements found in "Requirements for MPLS Network
Actions." This document follows the architectural framework for the
MPLS Network Actions (MNA) technologies specified in "MPLS Network
Actions (MNA) Framework."
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 21 September 2025.
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Post-Stack MNA Indicator in In-Stack MNA Sub-Stack . . . 5
3.2. Post-Stack MNA Encoding . . . . . . . . . . . . . . . . . 6
3.2.1. Post-Stack MNA Header . . . . . . . . . . . . . . . . 6
3.2.2. Post-Stack Network Action Encoding . . . . . . . . . 7
4. In-Stack Special Network Action Opcodes . . . . . . . . . . . 7
4.1. In-Stack Network Action Opcode for Post-Stack MNA Header
Offset . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. In-Stack Network Action Opcode for Post-Stack MNA Depth
Offset . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Processing Rules for P Bit . . . . . . . . . . . . . . . 8
5.2. Network Action Processing Order . . . . . . . . . . . . . 9
5.3. Node Capability Signaling . . . . . . . . . . . . . . . . 9
6. Nodes Processing Post-Stack Network Actions . . . . . . . . . 9
6.1. Encapsulating Node Responsibilities . . . . . . . . . . . 9
6.2. Transit Node Responsibilities . . . . . . . . . . . . . . 9
6.3. Penultimate Node Responsibilities . . . . . . . . . . . . 10
6.4. Decapsulating Node Responsibilities . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. Post-Stack MNA Header First Nibble . . . . . . . . . . . 10
8.2. In-Stack Network Action Opcodes . . . . . . . . . . . . . 10
8.3. Post-Stack MNA Header Types Registry . . . . . . . . . . 11
8.4. Post-Stack Network Action Opcodes . . . . . . . . . . . . 12
9. Appendix A: Examples . . . . . . . . . . . . . . . . . . . . 12
9.1. Examples of Post-Stack MNA Encoding . . . . . . . . . . . 12
9.1.1. NAS that only Indicates Post-Stack MNA . . . . . . . 12
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9.1.2. NAS that Indicates Post-Stack MNA Header Offset . . . 13
9.1.3. Post-Stack Network Action with Two Opcodes . . . . . 14
9.1.4. Post-Stack Network Action with two Different
Scopes . . . . . . . . . . . . . . . . . . . . . . . 15
9.2. In-Stack and Post-Stack Network Actions . . . . . . . . . 16
9.2.1. NAS with In-Stack and Post-Stack NAs . . . . . . . . 16
9.2.2. NASes with Different In-Stack and Post-Stack
Scopes . . . . . . . . . . . . . . . . . . . . . . . 17
9.2.3. Network Action Processing Order . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 20
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
[RFC3032] defines the encoding of the MPLS label stack, the basic
structure used to define a forwarding path. Forthcoming applications
require MPLS packets to perform special network actions and carry
optional Ancillary Data (AD) that can affect the packet forwarding
decision or trigger Operations, Administration, and Maintenance (OAM)
logging, for example. AD can be used to carry additional
information, such as for In Situ OAM (IOAM) as described in
[I-D.ietf-mpls-mna-usecases]. User-defined network actions allow
local actions to be defined. In some cases, more AD may be required
to be carried in the MPLS header, so these kinds of network actions
and their AD are encoded after the Bottom of Stack (BOS). This AD is
called Post-Stack Data.
This document defines the Post-Stack MPLS Network Action (MNA)
solution for carrying Network Actions and Ancillary Data after the
MPLS label stack. It is based on the In-Stack MNA solution defined
in [I-D.ietf-mpls-mna-hdr]. This solution document addresses the
Post-Stack network action and Post-Stack data specific requirements
found in [I-D.ietf-mpls-mna-requirements]. This document follows the
architectural framework for the MPLS Network Actions (MNA)
technologies specified in [I-D.ietf-mpls-mna-fwk].
2. Conventions Used in This Document
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
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2.2. Abbreviations
The terminology defined in [I-D.ietf-mpls-mna-fwk] and
[I-D.ietf-mpls-mna-requirements] are used in this document.
+============+=================+==================================+
|Abbreviation|Meaning | Reference |
+============+=================+==================================+
|AD |Ancillary Data | [I-D.ietf-mpls-mna-requirements] |
+------------+-----------------+----------------------------------+
|bSPL |Base Special | [RFC9017] |
| |Purpose Label | |
+------------+-----------------+----------------------------------+
|BOS |Bottom Of Stack | [RFC3032] |
+------------+-----------------+----------------------------------+
|HBH |Hop-By-Hop Scope | [I-D.ietf-mpls-mna-fwk] |
+------------+-----------------+----------------------------------+
|I2E |Ingress-To-Egress| [I-D.ietf-mpls-mna-fwk] |
| |Scope | |
+------------+-----------------+----------------------------------+
|IHS |I2E, HBH, or | [I-D.ietf-mpls-mna-hdr] |
| |Select Scope | |
+------------+-----------------+----------------------------------+
|ISD |In-Stack Data | [I-D.ietf-mpls-mna-requirements] |
+------------+-----------------+----------------------------------+
|LSE |Label Stack Entry| [RFC3032] |
+------------+-----------------+----------------------------------+
|MNA |MPLS Network | [I-D.ietf-mpls-mna-fwk] |
| |Actions | |
+------------+-----------------+----------------------------------+
|NAI |Network Action | [I-D.ietf-mpls-mna-requirements] |
| |Indicator | |
+------------+-----------------+----------------------------------+
|NAL |Network Action | [I-D.ietf-mpls-mna-hdr] |
| |Length | |
+------------+-----------------+----------------------------------+
|NAS |Network Action | [I-D.ietf-mpls-mna-fwk] |
| |Sub-Stack | |
+------------+-----------------+----------------------------------+
|NASL |Network Action | [I-D.ietf-mpls-mna-hdr] |
| |Sub-Stack Length | |
+------------+-----------------+----------------------------------+
|OAM |Operations, | [RFC6291] |
| |Administration, | |
| |and Maintenance | |
+------------+-----------------+----------------------------------+
|P |Post-Stack MNA | This document |
| |Indicator Bit | |
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+------------+-----------------+----------------------------------+
|PSD |Post-Stack Data | [I-D.ietf-mpls-mna-requirements] |
| | | and [I-D.ietf-mpls-mna-fwk] |
+------------+-----------------+----------------------------------+
|PS-MNA-OP |Post-Stack MPLS | This document |
| |Network Action | |
| |Opcode | |
+------------+-----------------+----------------------------------+
|TC |Traffic Class | [RFC5462] |
+------------+-----------------+----------------------------------+
|TTL |Time To Live | [RFC3032] |
+------------+-----------------+----------------------------------+
Table 1: Abbreviations
3. Overview
A flag in the In-Stack NAS header [I-D.ietf-mpls-mna-hdr] indicates
the presence of the Post-Stack MNA in the packet. The Post-Stack MNA
is encoded after the MPLS Label Stack (BOS), either immediately after
the BOS (i.e., start offset of 0) or after any other Post-Stack
headers that follow the BOS (i.e., start offset of non-zero).
The Post-Stack MNA solution contains two main parts:
* Post-Stack MNA Indicator in In-Stack MNA Sub-Stack
* Post-Stack MNA Encoding
3.1. Post-Stack MNA Indicator in In-Stack MNA Sub-Stack
A reserved bit (21st bit from the left in LSE Format B
[I-D.ietf-mpls-mna-hdr]) in the In-Stack MNA Sub-Stack described in
[I-D.ietf-mpls-mna-hdr] is used to indicate the presence of the Post-
Stack MNA in the packet after the BOS.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |P|IHS|S|U| NASL | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Post-Stack MNA Indicator in In-Stack MNA Sub-Stack
The following are the flags applicable to Post-Stack MNA encoding
purposes as defined in [I-D.ietf-mpls-mna-hdr].
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* P (1 Bit): Indicates the presence of the Post-Stack MNA in the
packet.
* IHS (2 Bit): Indicates the combined scope of the In-Stack and the
Post-Stack Network Actions. Each scope with P bit set will have
its corresponding Post-Stack MNA Header sub-stack.
* U (1 Bit): Indicates the combined Unknown Action Handling of the
In-Stack and the Post-Stack Network Actions.
3.2. Post-Stack MNA Encoding
The Post-Stack Network Action and its Ancillary Data are encoded
after the MPLS Label Stack (BOS). The Post-Stack Network Action may
carry multiple Post-Stack Network Actions and their corresponding
Ancillary Data.
This consist of two main parts:
* Post-Stack MNA Header
* Post-Stack Network Action Encoding
3.2.1. Post-Stack MNA Header
This header is the top-level header for all the Post-Stack Network
Actions that are encoded.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Post-Stack MNA Header
* NNNN (4 bits): This first nibble identifies the start of the Post-
Stack MNA Header [I-D.ietf-mpls-1stnibble]. A new value (value
TBA1) is assigned by IANA. Editor's note: Generic Associated
Channel (0001b) or CW (0000b) can be used.
* Version (4 bits): This is Post-Stack MNA Header version. The
initial version will be 0.
* PS-HDR-LEN (8 bits): Post-Stack MNA Header Total Length in 4-octet
units. This excludes the Post-Stack MNA Header.
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* TYPE (16 bits): Type is set to POST-STACK-HDR-MNA. The type value
is an IANA allocated value of 1.
3.2.2. Post-Stack Network Action Encoding
This header encodes a single Post-Stack Network Action. Using this
scheme, multiple Post-Stack Network Action and its corresponding
Ancillary data can be encoded.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP |R|R| PS-NAL | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Post-Stack Network Action Encoding
* PS-MNA-OP (7 bits): Post-Stack Network Action Opcode. Opcode "0"
is reserved and other opcodes will be assigned by IANA
accordingly.
* R (2 bits): Reserved bits.
* PS-NAL (7 bits): Post-Stack Network Action Length in 4-octet
units. This excludes the first 4-octets starting PS-MNA-OP.
* POST-STACK DATA (16 bits): Post-Stack Data associated with the
Post-Stack Network Action.
4. In-Stack Special Network Action Opcodes
4.1. In-Stack Network Action Opcode for Post-Stack MNA Header Offset
Opcode: TBA2
Purpose: This opcode carries the start offset of the Post-Stack MNA
Header from BOS.
LSE Format: B (defined in [I-D.ietf-mpls-mna-hdr])
Data: The data value of the LSE contains the offset from the MPLS BOS
in units of 4 octets. This allows the Generic Control Word (0000b)
[RFC4385] and G-ACh (0001b) [RFC5586] fields to be placed immediately
after the BOS. In the absence of this opcode, the Post-Stack MNA
Header is encoded immediately after the MPLS BOS. A data value of 1
indicates that the Post-Stack MNA Header starts 4 octets after the
BOS.
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Scope: This opcode can be used with any scope.
4.2. In-Stack Network Action Opcode for Post-Stack MNA Depth Offset
Opcode: TBA3
Purpose: This opcode carries the depth of the Post-Stack MNA offset
from BOS.
LSE Format: B or C (defined in [I-D.ietf-mpls-mna-hdr])
Data: The data value of the LSE contains the offset from the MPLS BOS
in units of 4 octets. A data value of 5 indicates that the Post-
Stack MNA ends 20 octets after the BOS.
Scope: This opcode can be used with any scope.
5. Procedure
5.1. Processing Rules for P Bit
The P bit MUST be set to 1 in In-Stack Network Action Sub-Stack when
Post-Stack MNA is added in the packet.
By default, the Post-Stack MNA Header starts immediately after the
BOS. The offset for the Post-Stack MNA Header that does not start
immediately after the BOS is indicated using the Post-Stack MNA
Header Offset Opcode TBA2.
The P bit MUST be set to 1 when the network action with opcode TBA2
is added to the In-Stack Network Action Sub-Stack. The node that
recognizes the network action with Opcode TBA2 MUST process the
packet according to the U flag if the P bit is not set.
The P bit MUST be set to 1 when the network action with opcode TBA3
is added to the In-Stack Network Action Sub-Stack. The node that
recognizes the network action with Opcode TBA3 MUST process the
packet according to the U flag if the P bit is not set.
The node that supports the P bit will process the Post-Stack Network
Actions in the Post-Stack MNA as defined in this document.
Conversely, the node that does not support the P bit will skip
processing the Post-Stack MNA altogether.
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5.2. Network Action Processing Order
The Post-Stack Network Actions are processed in the same order they
are encoded after the BOS. By default, they are processed after the
In-Stack Network Actions in the Network Action Sub-Stack. However,
Post-Stack Network Action Opcodes for applications (e.g., for IOAM
application, to be defined in future) can be added in the In-Stack
Network Action Sub-Stack to process Post-Stack Network Actions in a
certain order with respect to the Opcodes in the In-Stack Network
Action Sub-Stack.
5.3. Node Capability Signaling
The ingress node that is adding a Post-Stack MNA MUST ensure that the
egress node is capable of MNA and can remove the Post-Stack MNA from
the packet.
* Each participating node MUST signal the network actions that it
supports.
* Each participating node MUST signal its "Readable Label Depth
including Post-Stack MNA" that can be encoded.
The above capability signaling will be added in appropriate
protocols. Signaling details are outside the scope of this document.
6. Nodes Processing Post-Stack Network Actions
This section defines the specific responsibilities for nodes along an
MPLS path for processing Post-Stack Network Actions.
6.1. Encapsulating Node Responsibilities
The encapsulating node MAY add Post-Stack MNA to the packet in
accordance with its policies, the placement restrictions, and the
limitations.
The encapsulating node MUST NOT add a Post-Stack MNA to the packet if
the decapsulation node does not support Post-Stack MNA.
If the encapsulating node is also a transit node, then it MUST also
respect transit node responsibilities.
6.2. Transit Node Responsibilities
A transit node MAY modify the Ancillary Data in the Post-Stack MNA.
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A transit node MUST respect the Unknown Action Handling value encoded
in the NAS.
A node that removes the last copy of a NAS that has the P bit set
MUST remove all Post-Stack MNAs.
6.3. Penultimate Node Responsibilities
In addition to the transit node responsibilities above, the
penultimate node MUST NOT remove the last copy of an HBH or I2E NAS
when it is exposed after removing the forwarding (transport) label.
This allows the egress node to process the NAS.
6.4. Decapsulating Node Responsibilities
The decapsulating node MUST remove any Post-Stack MNA it receives.
7. Security Considerations
The security considerations in [RFC3032], [I-D.ietf-mpls-mna-fwk],
and [I-D.ietf-mpls-mna-hdr] also apply to this document.
8. IANA Considerations
8.1. Post-Stack MNA Header First Nibble
This document requests that IANA allocate a value (TBA1) for the
Post-Stack MNA Header Nibble (NNNN) from the registry "Post-Stack
First Nibble" created by [I-D.ietf-mpls-1stnibble] to indicate the
start of the Post-Stack MNA Header.
+=======+====================================+===============+
| Value | Description | Reference |
+=======+====================================+===============+
| TBA1 | Post-Stack MNA Header First Nibble | This document |
+-------+------------------------------------+---------------+
Table 2: Post-Stack First Nibble Registry
8.2. In-Stack Network Action Opcodes
The In-Stack Network Action Opcodes for In-Stack Network Action
Opcode registry (to be created by in [[I-D.ietf-mpls-mna-hdr]]) are
defined in the document as follows.
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+========+==========================================+===============+
| Opcode | Description | Reference |
+========+==========================================+===============+
| TBA2 | Offset of Start of Post-Stack MNA Header | This |
| | | document |
+--------+------------------------------------------+---------------+
| TBA3 | Offset of Depth of Post-Stack MNA | This |
| | | document |
+--------+------------------------------------------+---------------+
Table 3: In-Stack Network Action Flags With Ancillary Data Registry
8.3. Post-Stack MNA Header Types Registry
This document requests that IANA create a new registry with the name
"Post-Stack MNA Header Types". The registration procedure for this
registry is "IETF Review". The fields are "Type" (integer),
"Description" (string), and "Reference" (string). Type is an integer
0-65535.
The assignments for this registry are:
+=============+==============================+===============+
| Type | Description | Reference |
+=============+==============================+===============+
| 0 | Reserved, not to be assigned | This document |
+-------------+------------------------------+---------------+
| 1-65520 | IETF Review | This document |
+-------------+------------------------------+---------------+
| 65521-65524 | Experimental Use | This document |
+-------------+------------------------------+---------------+
| 65525-65535 | Private Use | This document |
+-------------+------------------------------+---------------+
Table 4: Post-Stack MNA Header Types Registry
The initial assignments for this registry are:
+======+====================+===============+
| Type | Description | Reference |
+======+====================+===============+
| 1 | POST-STACK-HDR-MNA | This document |
+------+--------------------+---------------+
Table 5: Post-Stack MNA Header Types
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8.4. Post-Stack Network Action Opcodes
This document requests that IANA create a new registry with the name
"Post-Stack Network Action Opcodes". The registration procedure for
this registry is "IETF Review". The fields are "Opcode" (integer),
"Description" (string), and "Reference" (string). Opcode is an
integer 0-127.
The initial assignments for this registry are:
+=========+==============================+===============+
| Opcode | Description | Reference |
+=========+==============================+===============+
| 0 | Reserved, not to be assigned | This document |
+---------+------------------------------+---------------+
| 1-110 | IETF Review | This document |
+---------+------------------------------+---------------+
| 111-114 | Experimental Use | This document |
+---------+------------------------------+---------------+
| 115-126 | Private Use | This document |
+---------+------------------------------+---------------+
Table 6: Post-Stack Network Action Opcodes Registry
9. Appendix A: Examples
9.1. Examples of Post-Stack MNA Encoding
9.1.1. NAS that only Indicates Post-Stack MNA
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|IHS|S|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP |R|R| PS-NAL=0 | PS ANCILLARY DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: NAS that only indicates Post-Stack MNA
In some cases, the NAS may encode only the presence of Post-Stack
MNA. The Post-Stack MNA Header starts immediately after the BOS.
9.1.2. NAS that Indicates Post-Stack MNA Header Offset
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=TBA2 | Post-Stack Offset = 2 |1|IHS|S|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP |R|R| PS-NAL=0 | PS ANCILLARY DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NAS Indicates Post-Stack MNA Header Offset
The NAS may encode the start offset for the Post-Stack MNA Header
with a non-zero value, for example, when it is after other header
such as GACH or CW header. In this example, the PSH starts at offset
of 8 bytes after the BoS.
9.1.3. Post-Stack Network Action with Two Opcodes
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|IHS|1|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=3 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP=2|R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP=3|R|R| PS-NAL=1 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Payload + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Post-Stack NA with Two Opcodes
This is an example, Post-Stack MNA encodes two different Post-Stack
Network Actions.
Details:
PS-HDR-LEN=3: This is the Total Length of Post-Stack MNA.
PS-MNA-OP=2: Post-Stack MNA Opcode "2".
PS-NAL=0: Post-Stack Network Action does not contain any
additional data.
PS-MNA-OP=3: Post-Stack MNA Opcode "3".
PS-NAL=1: Post-Stack Network Action contains 1 additional 4-octet
Ancillary data.
9.1.4. Post-Stack Network Action with two Different Scopes
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|HBH|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=TBA2 | Post-Stack Offset = 2 |1|I2E|1|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP=2|R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=2 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP=3|R|R| PS-NAL=1 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Payload + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Post-Stack NA with two Different Scopes
This is an example of Post-Stack MNA encoding, that encode two
different different scoped Post-Stack Network Actions. The first
scope is Hop-By-Hop and the second scope is Ingress-To-Egress scoped
Post-Stack Network Action.
Details:
The offset of the Hop-By-Hop scoped Post-Stack Network Action 0.
Opcode TBA2 carries the offset of the Ingress-To-Egress scoped
Post-Stack Network Action. The data is "2," i.e., the Post-Stack
MNA Header starts 8 bytes after the MPLS Bottom of Stack.
9.2. In-Stack and Post-Stack Network Actions
9.2.1. NAS with In-Stack and Post-Stack NAs
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |1|IHS|S|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: NAS with In-Stack and Post-Stack NAs
In some cases, the NAS may encode In-Stack NAs and indicate the
presence of Post-Stack MNA Header. The IHS field indicates the scope
of both the In-Stack and Post-Stack NAs.
9.2.2. NASes with Different In-Stack and Post-Stack Scopes
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |0|HBH|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|I2E|1|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS-MNA-OP |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 9: NASes with Different In-Stack and Post-Stack Scopes
In some cases the label stack may need to carry In-Stack NAs with
Hop-By-Hop scope and Post-Stack NAs with I2E scope. In this case,
there will be two NASes in the label stack. In this case, the first
NAS will encode the In-Stack NA with the Hop-By-Hop scope and the
second NAS will encode the presence of I2E scoped Post-Stack NAs.
9.2.3. Network Action Processing Order
The Post-Stack NA opcode can be added to interleave Post-Stack
network actions with In-Stack network actions. The following example
shows how to process the Post-Stack NA before the In-Stack NA.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |1|IHS|0|U| NASL=3|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |0|U| NAIs |NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=IOAMPS| Post-Stack Offset=1 |0|U|PS-NAI |NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=7 | Ancillary Data |1|U| AD |NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PS-OP=IOAMPS |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Post-Stack and In-Stack NA Processing Order
In this example, opcode 8 is processed first, followed by the Flag-
Based NAIs, then the Post-Stack NA Opcode IOAMPS (which has an offset
of 1 word, i.e., 4 bytes), and finally opcode 7.
10. References
10.1. Normative References
[I-D.ietf-mpls-mna-fwk]
Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions (MNA) Framework", Work in Progress,
Internet-Draft, draft-ietf-mpls-mna-fwk-15, 27 December
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
mpls-mna-fwk-15>.
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[I-D.ietf-mpls-mna-requirements]
Bocci, M., Bryant, S., and J. Drake, "Requirements for
Solutions that Support MPLS Network Actions (MNA)", Work
in Progress, Internet-Draft, draft-ietf-mpls-mna-
requirements-16, 30 May 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-requirements-16>.
[I-D.ietf-mpls-mna-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K.
Kompella, "MPLS Network Action (MNA) Sub-Stack Solution",
Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr-
12, 3 March 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-mpls-mna-hdr-12>.
[I-D.ietf-mpls-1stnibble]
Kompella, K., Bryant, S., Bocci, M., Mirsky, G.,
Andersson, L., and J. Dong, "IANA Registry and Processing
Recommendations for the First Nibble Following a Label
Stack", Work in Progress, Internet-Draft, draft-ietf-mpls-
1stnibble-13, 5 December 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
1stnibble-13>.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
February 2006, <https://www.rfc-editor.org/info/rfc4385>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
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[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/info/rfc6291>.
[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>.
[RFC9017] Andersson, L., Kompella, K., and A. Farrel, "Special-
Purpose Label Terminology", RFC 9017,
DOI 10.17487/RFC9017, April 2021,
<https://www.rfc-editor.org/info/rfc9017>.
10.2. Informative References
[I-D.ietf-mpls-mna-usecases]
Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use
Cases for MPLS Network Action Indicators and MPLS
Ancillary Data", Work in Progress, Internet-Draft, draft-
ietf-mpls-mna-usecases-15, 23 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-usecases-15>.
Acknowledgments
The authors would like to thank the authors and contributors of the
draft-ietf-mpls-mna-hdr as this document borrows some text from the
earlier version of that document. The authors would like to thank
Greg Mirsky, Loa Andersson, Haoyu Song, and Joel Halpern for
reviewing this document and providing many useful comments.
Contributors
The following people have substantially contributed to this document:
Jisu Bhattacharya
Cisco Systems, Inc.
Email: jisu@cisco.com
John Drake
Juniper Networks
United States
Email: jdrake@juniper.net
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Authors' Addresses
Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
Email: jrajaman@cisco.com
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Royi Zigler
Broadcom
Email: royi.zigler@broadcom.com
Tony Li
Juniper Networks
Email: tony.li@tony.li
Jie Dong
Huawei Technologies
Beijing
China
Email: jie.dong@huawei.com
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