Internet-Draft Post-Stack MNA Solution May 2025
Rajamanickam, et al. Expires 1 December 2025 [Page]
Workgroup:
MPLS Working Group
Internet-Draft:
draft-ietf-mpls-mna-ps-hdr-01
Published:
Intended Status:
Standards Track
Expires:
Authors:
J. Rajamanickam, Ed.
Cisco Systems, Inc.
R. Gandhi, Ed.
Cisco Systems, Inc.
R. Zigler
Broadcom
T. Li
Juniper Networks
J. Dong
Huawei Technologies

Post-Stack MPLS Network Action (MNA) Solution

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 time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 1 December 2025.

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Table of Contents

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 network action with 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.

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.

Table 1: Abbreviations
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 Header Presence Bit This document
PSD Post-Stack Data [I-D.ietf-mpls-mna-requirements] and [I-D.ietf-mpls-mna-fwk]
PSH Post-Stack Header This document
TC Traffic Class [RFC5462]
TTL Time To Live [RFC3032]

3. Overview

The Post-Stack MNA solution contains two main parts:

3.1. Post-Stack Header Presence 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 Network Action Sub-Stack (NASS) described in [I-D.ietf-mpls-mna-hdr] is defined as P bit in this document to indicate the presence of the Post-Stack Header in the packet after the BOS.

The Post-Stack Header 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).

 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 Header Presence in In-Stack MNA Sub-Stack

The following flags as defined in [I-D.ietf-mpls-mna-hdr] are also applicable to Post-Stack Header:

  • IHS (2 Bit): Indicates the combined scope of the In-Stack and the Post-Stack Network Actions. NASS for each scope with P bit set will have its corresponding Post-Stack Header.
  • U (1 Bit): Indicates the combined Unknown Action Handling of the In-Stack and the Post-Stack Network Actions.

3.2. Post-Stack Header Encoding

The Post-Stack Header is encoded after the Bottom of the MPLS Label Stack (BOS). The Post-Stack Header carry one ore more Post-Stack Network Actions and their Ancillary Data.

The PSH consist of two main parts:

  • Post-Stack Header (PSH) Type
  • Post-Stack Network Action Encoding

3.2.1. Post-Stack Header Type

The Post-Stack Header type is the top-header for all the Post-Stack Network Actions that are encoded in the PSH for each scope.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN    | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Post-Stack Header Type
  • TBA1 (4 bits): This first nibble [I-D.ietf-mpls-1stnibble] identifies the start of the PSH. A new value (value TBA1) is to be assigned by IANA for PSH. Editor's note: Generic Associated Channel (0001b) or CW (0000b) can be used.
  • Version (4 bits): This is PSH version. The initial version is set to 0.
  • PS-HDR-LEN (8 bits): PSH Total Length in 4-octet units that includes Post-Stack Network Actions. This excludes the PSH type header.
  • TYPE (16 bits): Type is set to MNA-POST-STACK-HDR as value 1 for MNA, to be allocated by IANA.

3.2.2. Post-Stack Network Action Encoding

The format shown in Figure 3, encodes a single Post-Stack Network Action. By repeating this format, 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-OP  |R|R|  PS-NAL     |       POST-STACK DATA         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Post-Stack Network Action Encoding
  • MNA-PS-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 MNA-PS-OP.
  • POST-STACK DATA (16 bits): Post-Stack Data associated with the Post-Stack Network Action.

4. In-Stack Network Action Special Opcodes

4.1. In-Stack Network Action Opcode for PSH Start Offset

Opcode: TBA2

Purpose: This opcode carries the start offset of the PSH 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 PSH is encoded immediately after the MPLS BOS. A data value of 1 indicates that the PSH starts 4 octets after the BOS.

Scope: This opcode can be used with any scope.

4.2. In-Stack Network Action Opcode for PSH Depth Offset

Opcode: TBA3

Purpose: This opcode carries the depth of the Post-Stack Header 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 Header 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 corresponding Post-Stack Header is added in the packet.

By default, the PSH starts immediately after the BOS. The offset for the PSH that does not start immediately after the BOS is indicated using the PSH Start 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, processes the Post-Stack Network Actions in the Post-Stack Header as defined in this document. Conversely, the node that does not support the P bit, will skip processing the Post-Stack Header altogether.

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 (such as IOAM as described in [I-D.ietf-mpls-mna-usecases]) 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 Header MUST ensure that the egress node is capable of Post-Stack MNA and can remove the PSH 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 Header" that can be encoded.

The above capability signaling will be added in appropriate protocols. Signaling details are outside the scope of this document.

6. Node Responsibilities

This section defines the specific responsibilities for nodes along an MPLS path for processing a Post-Stack Header.

6.1. Encapsulating Node Responsibilities

The encapsulating node MAY add Post-Stack Header to the packet in accordance with its policies, the placement restrictions, and the limitations.

The encapsulating node MUST NOT add a Post-Stack Header to the packet if the decapsulation node does not support Post-Stack Header.

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 Header.

A transit node MUST respect the Unknown Action Handling flag encoded in the corresponding NAS when processing the PSH.

A node that removes the last copy of a NAS that has the P bit set MUST remove all Post-Stack Headers.

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 and associated PSH when it is exposed after removing the forwarding (transport) label. This allows the egress node to process the NAS and associated PSH.

6.4. Decapsulating Node Responsibilities

The decapsulating node MUST remove any Post-Stack Header 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. First Nibble for Post-Stack Header

This document requests that IANA allocate a value (TBA1) for the First Nibble (value TBA1) for Post-Stack Header from the registry "Post-Stack First Nibble" created by [I-D.ietf-mpls-1stnibble] to indicate the start of the PSH after BOS.

Table 2: First Nibble for Post-Stack Header
Value Description Reference
TBA1 First Nibble for Post-Stack Header This document

8.2. Post-Stack Header Types Registry

This document requests that IANA create a new registry with the name "Post-Stack Header Types" as follows. The registration procedure for this registry is "IETF Review", "Experimental Use" and "Private Use". The fields are "Type" (integer), "Description" (string), and "Reference" (string).

The assignments for this registry are:

Table 3: Post-Stack Header Types Registry
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 assignment for this registry is:

Table 4: Post-Stack Header Type For MNA
Type Description Reference
1 Post-Stack Header Type For MNA This document

8.3. In-Stack Network Action Opcodes

The opcodes for In-Stack Network Action to be allocated by IANA from the "In-Stack Network Action Opcode registry" to be created by in [[I-D.ietf-mpls-mna-hdr]] as defined in this document as follows.

Table 5: In-Stack Network Action Opcodes
Opcode Description Reference
TBA2 Offset for Start of Post-Stack Header This document
TBA3 Offset for Depth of Post-Stack Header This document

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", "Experimental Use" and "Private Use". The fields are "Opcode" (integer), "Description" (string), and "Reference" (string). Opcode is an integer 0-127.

The assignments for this registry are:

Table 6: Post-Stack Network Action Opcodes Registry
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
127 Reserved, not to be assigned This document

9. Appendix A: Examples

9.1. Examples of Post-Stack Header Encoding

9.1.1. NAS that only Indicates Post-Stack Header 

 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|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                             [0|               ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                             |1|               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=1  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-OP  |R|R|  PS-NAL=0   |       POST-STACK DATA         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                                               ~
~                           Payload                             ~
~                                                               ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: NAS that only indicates Post-Stack Header

In some cases, the NAS may encode only the presence of Post-Stack Header. The Post-Stack Header starts immediately after the BOS.

9.1.2. NAS that Indicates Post-Stack Header Start Offset 

 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=TBA2 |  Post-Stack Offset = 2  |1|IHS|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                             [0|               ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                             |1|               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=1  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-OP  |R|R|  PS-NAL=0   |       POST-STACK DATA         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                                               ~
~                           Payload                             ~
~                                                               ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NAS Indicates Post-Stack Header Start Offset

The NAS may encode the start offset for the Post-Stack 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 Actions with Two Opcodes 

 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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=3  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-OP=2|R|R|  PS-NAL=0   |       POST-STACK DATA         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-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 Header encodes two different Post-Stack Network Actions.

Details:

  • PS-HDR-LEN=3: This is the Total Length of Post-Stack Header.
  • MNA-PS-OP=2: Post-Stack NA Opcode 2.
  • PS-NAL=0: Post-Stack Network Action does not contain any additional data.
  • MNA-PS-OP=3: Post-Stack NA 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 

 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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=1  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-OP=2|R|R|  PS-NAL=0   |       POST-STACK DATA         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=2  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-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 Header 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 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 

 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       |1|IHS|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                             [0|               ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                             |1|               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=1  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-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 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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1  |Version| PS-HDR-LEN=1  | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  MNA-PS-OP  |R|R|  PS-NAL=0   |       POST-STACK DATA         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                                               ~
~                           Payload                             ~
~                                                               ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.

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, , <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-mna-fwk-15>.
[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, , <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, , <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, , <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, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc5586>.
[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, , <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, , <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, , <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, , <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

Authors' Addresses

Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Royi Zigler
Broadcom
Tony Li
Juniper Networks
Jie Dong
Huawei Technologies
Beijing
China