| Internet-Draft | Post-Stack MNA Solution | March 2025 |
| Rajamanickam, et al. | Expires 21 September 2025 | [Page] |
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."¶
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[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].¶
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.¶
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 Purpose Label | [RFC9017] |
| BOS | Bottom Of Stack | [RFC3032] |
| HBH | Hop-By-Hop Scope | [I-D.ietf-mpls-mna-fwk] |
| I2E | Ingress-To-Egress Scope | [I-D.ietf-mpls-mna-fwk] |
| IHS | I2E, HBH, or Select Scope | [I-D.ietf-mpls-mna-hdr] |
| ISD | In-Stack Data | [I-D.ietf-mpls-mna-requirements] |
| LSE | Label Stack Entry | [RFC3032] |
| MNA | MPLS Network Actions | [I-D.ietf-mpls-mna-fwk] |
| NAI | Network Action Indicator | [I-D.ietf-mpls-mna-requirements] |
| NAL | Network Action Length | [I-D.ietf-mpls-mna-hdr] |
| NAS | Network Action Sub-Stack | [I-D.ietf-mpls-mna-fwk] |
| NASL | Network Action Sub-Stack Length | [I-D.ietf-mpls-mna-hdr] |
| OAM | Operations, Administration, and Maintenance | [RFC6291] |
| P | Post-Stack MNA Indicator Bit | This document |
| PSD | Post-Stack Data | [I-D.ietf-mpls-mna-requirements] and [I-D.ietf-mpls-mna-fwk] |
| PS-MNA-OP | Post-Stack MPLS Network Action Opcode | This document |
| TC | Traffic Class | [RFC5462] |
| TTL | Time To Live | [RFC3032] |
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:¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following are the flags applicable to Post-Stack MNA encoding purposes as defined in [I-D.ietf-mpls-mna-hdr].¶
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:¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
Scope: This opcode can be used with any scope.¶
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.¶
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.¶
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.¶
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.¶
The above capability signaling will be added in appropriate protocols. Signaling details are outside the scope of this document.¶
This section defines the specific responsibilities for nodes along an MPLS path for processing Post-Stack Network Actions.¶
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.¶
A transit node MAY modify the Ancillary Data in the Post-Stack MNA.¶
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.¶
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.¶
The decapsulating node MUST remove any Post-Stack MNA it receives.¶
The security considerations in [RFC3032], [I-D.ietf-mpls-mna-fwk], and [I-D.ietf-mpls-mna-hdr] also apply to this document.¶
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 |
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.¶
| Opcode | Description | Reference |
|---|---|---|
| TBA2 | Offset of Start of Post-Stack MNA Header | This document |
| TBA3 | Offset of Depth of Post-Stack MNA | This document |
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 |
The initial assignments for this registry are:¶
| Type | Description | Reference |
|---|---|---|
| 1 | POST-STACK-HDR-MNA | This document |
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 |
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 ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In some cases, the NAS may encode only the presence of Post-Stack MNA. The Post-Stack MNA Header starts immediately 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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 ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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 | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is an example, Post-Stack MNA encodes two different Post-Stack Network Actions.¶
Details:¶
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 | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:¶
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 ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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 ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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.¶
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¶