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Post-Stack MPLS Network Action (MNA) Solution
draft-jags-mpls-ps-mna-hdr-03

Document Type Active Internet-Draft (individual)
Authors Jaganbabu Rajamanickam , Rakesh Gandhi , Royi Zigler , Tony Li , Jie Dong
Last updated 2024-06-25
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draft-jags-mpls-ps-mna-hdr-03
MPLS Working Group                                  J. Rajamanickam, Ed.
Internet-Draft                                            R. Gandhi, Ed.
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: 27 December 2024                                      R. Zigler
                                                                Broadcom
                                                                   T. Li
                                                        Juniper Networks
                                                                 J. Dong
                                                     Huawei Technologies
                                                            25 June 2024

             Post-Stack MPLS Network Action (MNA) Solution
                     draft-jags-mpls-ps-mna-hdr-03

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 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
   (PSD) 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 27 December 2024.

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Copyright Notice

   Copyright (c) 2024 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
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   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 . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Post-Stack Network Action Indicator . . . . . . . . . . . . .   5
   5.  Post-Stack Network Action Encoding  . . . . . . . . . . . . .   6
     5.1.  Post-Stack Header . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Post-Stack Network Action Header  . . . . . . . . . . . .   6
   6.  In-Stack Special Opcode Allocation  . . . . . . . . . . . . .   7
     6.1.  Post-Stack Header Offset  . . . . . . . . . . . . . . . .   7
     6.2.  PS-IS-NA Ordering . . . . . . . . . . . . . . . . . . . .   8
   7.  Node Capability Signaling . . . . . . . . . . . . . . . . . .   8
   8.  Processing the Network Action Sub-Stack . . . . . . . . . . .   8
     8.1.  Encapsulating Node Responsibilities . . . . . . . . . . .   9
     8.2.  Transit Node Responsibilities . . . . . . . . . . . . . .   9
     8.3.  Penultimate Node Responsibilities . . . . . . . . . . . .   9
     8.4.  Decapsulating Node Responsibilities . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Post-Stack Header First Nibble . . . . . . . . . . . . .  10
     10.2.  In-Stack Network Action Opcodes  . . . . . . . . . . . .  10
     10.3.  Post-Stack Header Types Registry . . . . . . . . . . . .  11
     10.4.  Post-Stack Network Action Opcodes  . . . . . . . . . . .  11
   11. Appendix A: Examples  . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Post-Stack Network Action Encoding . . . . . . . . . . .  12
       11.1.1.  NAS that only Indicates Post-Stack NAs . . . . . . .  12
       11.1.2.  NAS with both In-Stack and Post-Stack NAs  . . . . .  12
       11.1.3.  NASes with Different ISD and PSD Scope . . . . . . .  13
     11.2.  Post-Stack Network Action with two Opcodes . . . . . . .  14
     11.3.  Post-Stack Network Action with two different scopes  . .  15
     11.4.  Network Action Processing Order  . . . . . . . . . . . .  16

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       11.4.1.  Post-Stack NA Processing Order . . . . . . . . . . .  17
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     12.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  19
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

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 OAM logging, for example.  Ancillary Data can be
   used to carry additional information, such as a IOAM, Path tracing
   etc.  Several MNA applications are described in
   [I-D.ietf-mpls-mna-usecases].  User-defined network actions allow
   new, local actions to be defined.  In some cases, more Ancillary Data
   may required to be carried in the MPLS header, so these kind of
   Network Actions and its Ancillary data are encoded after the MPLS
   Stack.  These are called as Post-Stack Data.

   This document defines the syntax and semantics of Post-Stack Network
   Actions and their corresponding Ancillary Data based on the In-Stack
   MNA solution defined in [I-D.ietf-mpls-mna-hdr].  This document
   addresses the requirements specified in
   [I-D.ietf-mpls-mna-requirements].  This document follows the
   framework 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.

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    +============+=================+==================================+
    |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       | This document                    |
    |            |Network Action   |                                  |
    |            |Indicator Bit    |                                  |
    +------------+-----------------+----------------------------------+
    |PSD         |Post-Stack Data  | [I-D.ietf-mpls-mna-requirements] |
    |            |                 | and [I-D.ietf-mpls-mna-fwk]      |
    +------------+-----------------+----------------------------------+

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    |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.  The Post-Stack MNA's are encoded
   after the MPLS Label Stack (BoS).

   The Post-Stack MNA encoding contains two main parts:

   *  Post-Stack Network Action Indicator

   *  Post-Stack Network Action Encoding

4.  Post-Stack Network Action Indicator

   A reserved bit (21st bit from left in LSE Format B
   [I-D.ietf-mpls-mna-hdr]) in the In-Stack MNA header described in
   [I-D.ietf-mpls-mna-hdr] is used to indicate the presence of the Post-
   Stack Network Action.

    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 Network Action Indicator

   The below are the flags applicable to Post-Stack MNA encoding
   purposes defined in [I-D.ietf-mpls-mna-hdr].

   *  P (1 Bit) : Indicates the presence of the Post-Stack MNA

   *  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 sub-stack.

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   *  U (1 Bit) : Indicates the combined Unknown Action Handling of the
      In-Stack and the Post-Stack Network Actions

5.  Post-Stack Network Action 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 its corresponding
   Ancillary Data.

   This consist of two main parts:

   *  Post-Stack Header

   *  Post-Stack Network Action Header

5.1.  Post-Stack 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 Header

   *  NNNN (4 bits): This first nibble identifies the start of the Post-
      Stack Header.  A new value can be assigned by IANA (value TBA1).
      Generic Associated Channel (0001b) or CW (0000b) can be used
      instead.

   *  Version (4 bits): This is Post-Stack Header version.  The initial
      version will be 0.

   *  PS-HDR-LEN (8 bits): Post-Stack Header Total Length in 4-octet
      units.  This excludes the Post-Stack Header.

   *  TYPE (16 bits): Type is set to POST-STACK-HDR-MNA.  The type value
      is an IANA allocated value of 1.

5.2.  Post-Stack Network Action Header

   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.

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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  PS-MNA-OP  |R|U|  PS-NAL     |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: Post-Stack Network Action Header

   *  PS-MNA-OP (7 bits): Post-Stack Network Action Opcode.  Opcode "0"
      is reserved and other opcodes will be assigned by IANA
      accordingly.

   *  R (1 bit): Reserved bit.

   *  U (1 bit): Unknown Post-Stack Network Action Handling bit.

   *  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.

6.  In-Stack Special Opcode Allocation

   Some of the In-Stack MNA Opcodes are allocated to support Post-Stack
   Network Action.  They are as follows.

6.1.  Post-Stack Header Offset

   Opcode: TBA2

   Purpose: This opcode carries the start offset of the Post-Stack
   Header.

   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.  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 Header
   is encoded immediately after the MPLS BOS.  A data value of 1
   indicates that the Post-Stack Header starts 4 octets after the BOS.

   Scope: This opcode can be used with any scope.

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6.2.  PS-IS-NA Ordering

   Opcode: TBA3

   Purpose: In cases where the ordering of network action is significant
   and where some of the network actions reside in Post-Stack Network
   Action, this opcode can be used to insert Post-Stack network actions
   into the order of execution.  The 'P' bit and 'O' bit MUST be set in
   the NAS's Format B LSE [I-D.ietf-mpls-mna-hdr]) if this opcode is
   used.

   LSE Format: B, C, D (defined in [I-D.ietf-mpls-mna-hdr])

   Data: The data field contains one or more 7-bit Post-Stack MNA
   Opcode.  When used with LSE Format B, only one PS MNA Opcode is
   carried.  Two PS MNA opcodes can be carried in a Format C LSE.  If
   Format D LSEs [I-D.ietf-mpls-mna-hdr]) are used, each may carry up to
   three PS MNA opcodes.  The PS MNA opcodes are the stored concatenated
   in the most significant bits of the data field.  If multiple
   indicators are carried, the most significant PS MNA opcode is
   evaluated to the least significant.  PS MNA opcodes do not span LSEs.
   If some PS MNA opcode positions are not to be used, then the opcode
   should be set to value 0.

   Scope: This opcode can be used with any scope.

7.  Node Capability Signaling

   The ingress node which is adding a Post-Stack MNA MUST make sure that
   the egress node is capable of MNA and removes the Post-Stack MNA.

   *  Each participating node MUST signal the network actions that it
      supports.

   *  Each participating node MUST signal its Maximum Post-Stack MNA
      Length that could encoded.

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

8.  Processing the Network Action Sub-Stack

   This section defines the specific responsibilities for nodes along a
   MPLS path.

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8.1.  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.

8.2.  Transit Node Responsibilities

   A transit node MAY change 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 Network Actions.

8.3.  Penultimate Node Responsibilities

   In addition to the transit node responsibilities above, the
   penultimate node MUST NOT remove the last copy of a HBH or I2E NAS
   when it is exposed after removing the forwarding (transport) label.
   This allows the egress node to process the NAS.

8.4.  Decapsulating Node Responsibilities

   The decapsulating node MUST remove any Post-Stack MNA it receives.

9.  Security Considerations

   The security considerations in [RFC3032] also apply to this document.

   In addition, MNA creates a new dimension in security concerns:

   *  The actions of an encapsulating node can affect any or all of the
      nodes along the path.  In the most common and benign situations,
      such as a syntactically incorrect packet, this could result in
      packet loss or corruption.

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   *  The semantics of a network action are unbounded and may be
      insecure.  A network action could be defined that made arbitrary
      changes to the memory of the forwarding router, which could then
      be used by the encapsulating node to compromise every MNA capable
      router in the network.  The IETF needs to ensure that only secure
      network actions are defined.

   *  The MNA architecture supports locally defined network actions.
      For such actions, there will be limited oversight to ensure that
      the semantics do not create security issues.  Implementors and
      network operators will need to ensure that locally defined network
      actions do not compromise the security of the network.

10.  IANA Considerations

10.1.  Post-Stack Header First Nibble

   This document requests that IANA allocate a value (TBA1) for the
   Post-Stack 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 Header.

        +=======+================================+===============+
        | Value | Description                    | Reference     |
        +=======+================================+===============+
        | TBA1  | Post-Stack Header First Nibble | This document |
        +-------+--------------------------------+---------------+

                Table 2: Post-Stack First Nibble Registry

10.2.  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.

     +========+======================================+===============+
     | Opcode | Description                          | Reference     |
     +========+======================================+===============+
     | TBA2   | Offset of start of Post-Stack Header | This document |
     +--------+--------------------------------------+---------------+
     | TBA3   | PS-IS-NA Ordering                    | This document |
     +--------+--------------------------------------+---------------+

         Table 3: In-Stack Network Action Flags With Ancillary Data
                                  Registry

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10.3.  Post-Stack Header Types Registry

   This document requests that IANA create a new registry with the name
   "Post-Stack 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 Header Types Registry

   The initial assignments for this registry are:

               +======+====================+===============+
               | Type |    Description     | Reference     |
               +======+====================+===============+
               | 1    | POST-STACK-HDR-MNA | This document |
               +------+--------------------+---------------+

                      Table 5: Post-Stack Header Types

10.4.  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:

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        +=========+==============================+===============+
        | 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

11.  Appendix A: Examples

11.1.  Post-Stack Network Action Encoding

11.1.1.  NAS that only Indicates 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Label=MNA bSPL              | TC  |S|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Opcode=TBA2|    Offset = 0           |P|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|U|  PS-NAL=0   |       PS ANCILLARY DATA       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~                           Payload                             ~
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 4: NAS encoding only Post-Stack NAs

   In some cases, the NAS may encode only the presence of Post-Stack
   NAs.  The IHS field indicates the scope of the Post-Stack NAs (I2E,
   HBH, Select).

11.1.2.  NAS with both 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=TBA2 |   Offset = 0            |P|IHS|0|U| NASL=1|NAL=0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=1    |        Flag-Based NAIs        |S|U| NAIs  |NAL=0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                             |1|               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |N N N N|Version|  PS-HDR-LEN=1 |    TYPE = POST-STACK-HDR-MNA  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  PS-MNA-OP  |R|U|  PS-NAL=0   |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~                           Payload                             ~
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 5: 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 NAs.  The NASL is set to "1", indicating the
   presence of one additional LSE.  The IHS field indicates the scope of
   both the In-Stack and Post-Stack NAs.

11.1.3.  NASes with Different ISD and PSD Scope

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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=1 |  Flag-Baed NAIs            |P|HBH|0|U| NASL=0|NAL=0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=TBA2 |   Offset = 0            |P|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|U|  PS-NAL=0   |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~                           Payload                             ~
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 6: NASes with Different ISD and PSD Scope

   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.

11.2.  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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=TBA2 |   Offset = 0            |P|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|U|  PS-NAL=0   |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  PS-MNA-OP=3|R|U|  PS-NAL=1   |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       POST-STACK DATA                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Optional Payload + Padding                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 7: Post-Stack NA Example with two Opcodes

   This is an example of Post-Stack MNA encoding, that encode two
   different Post-Stack Network Actions.

   Details:

      PS-HDR-LEN=3: This is the Total Length of Post-Stack MNAs.

      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.

11.3.  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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=TBA2 |   Offset = 0            |P|HBH|0|U| NASL=0|NAL=0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=TBA2 |   Offset = 2            |P|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|U|  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|U|  PS-NAL=1   |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      POST-STACK DATA                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Optional Payload + Padding                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8: Post-Stack NA Example 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
   PSD data.

   Details:

      First Opcode:TBA2: This the offset of the Hop-By-Hop scoped PSD
      data.  This value of this opcode is "0"

      Second Opcode:TBA2: This the offset of the Ingress-To-Egress
      scoped PSD data.  This value of this opcode is "2" (i.e) the PSD
      stack starts from second 4-octet unit after the MPLS Bottom Of
      Stack

11.4.  Network Action Processing Order

   The semantics of a network action can vary widely and the results of
   processing one network action may affect the processing of a
   subsequent network action.

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11.4.1.  Post-Stack NA Processing Order

   By default, Post-Stack NAs follow the ordering of the encoding.
   However, the PS-IS-NA ordering opcode can be used to override the
   default ordering and interleave Post-Stack network actions with In-
   Stack network actions.

   In some cases, Post-Stack NAs needs to be processed before In-Stack
   NAs.  This section shows how to prioritize the Post-Stack NAs over
   In-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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Label=MNA bSPL               | TC  |0|    TTL        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=8    |      Ancillary Data     |P|IHS|0|U| NASL=3|NAL=0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=1    |      Flag-Based NAIs          |0|U| NAIs  |NAL=0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Opcode=TBA3 |      Post-Stack NA=6          |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-MNA-OP=6 |R|U|  PS-NAL=0   |       POST-STACK DATA         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 9: Post-Stack and In-Stack NA processing order

   In the above example, opcode 8 is processed first, then the Flag-
   Based NAIs, followed by Post-Stack NA Opcode 6, and finally opcode 7.

12.  References

12.1.  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-09, 19 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
              mna-fwk-09>.

   [I-D.ietf-mpls-mna-requirements]
              Bocci, M., Bryant, S., and J. Drake, "Requirements for
              Solutions that Support MPLS Network Actions (MNA)", Work

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              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-
              07, 17 June 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-mpls-mna-hdr-07>.

   [I-D.ietf-mpls-1stnibble]
              Kompella, K., Bryant, S., Bocci, M., Mirsky, G.,
              Andersson, L., and J. Dong, "IANA Registry for the First
              Nibble Following a Label Stack", Work in Progress,
              Internet-Draft, draft-ietf-mpls-1stnibble-08, 18 June
              2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
              mpls-1stnibble-08>.

   [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>.

12.2.  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-10, 20 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
              mna-usecases-10>.

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 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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