MPLS Working Group J. Rajamanickam, Ed. Internet-Draft R. Gandhi, Ed. Intended status: Standards Track Cisco Systems, Inc. Expires: 21 September 2025 R. Zigler Broadcom T. Li Juniper Networks J. Dong Huawei Technologies 20 March 2025 Post-Stack MPLS Network Action (MNA) Solution draft-jags-mpls-ps-mna-hdr-05 Abstract This document defines the Post-Stack MPLS Network Action (MNA) solution for carrying Network Actions and Ancillary Data after the MPLS label stack, based on the In-Stack MNA solution defined in "MPLS Network Action (MNA) Sub-Stack Solution." MPLS Network Actions can be used to influence packet forwarding decisions, carry additional Operations, Administration, and Maintenance (OAM) information in the MPLS packet, or perform user-defined operations. This solution document addresses the Post-Stack network action and Post-Stack data specific requirements found in "Requirements for MPLS Network Actions." This document follows the architectural framework for the MPLS Network Actions (MNA) technologies specified in "MPLS Network Actions (MNA) Framework." Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 21 September 2025. Rajamanickam, et al. Expires 21 September 2025 [Page 1] Internet-Draft Post-Stack MNA Solution March 2025 Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components 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 . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Post-Stack MNA Indicator in In-Stack MNA Sub-Stack . . . 5 3.2. Post-Stack MNA Encoding . . . . . . . . . . . . . . . . . 6 3.2.1. Post-Stack MNA Header . . . . . . . . . . . . . . . . 6 3.2.2. Post-Stack Network Action Encoding . . . . . . . . . 7 4. In-Stack Special Network Action Opcodes . . . . . . . . . . . 7 4.1. In-Stack Network Action Opcode for Post-Stack MNA Header Offset . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. In-Stack Network Action Opcode for Post-Stack MNA Depth Offset . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1. Processing Rules for P Bit . . . . . . . . . . . . . . . 8 5.2. Network Action Processing Order . . . . . . . . . . . . . 9 5.3. Node Capability Signaling . . . . . . . . . . . . . . . . 9 6. Nodes Processing Post-Stack Network Actions . . . . . . . . . 9 6.1. Encapsulating Node Responsibilities . . . . . . . . . . . 9 6.2. Transit Node Responsibilities . . . . . . . . . . . . . . 9 6.3. Penultimate Node Responsibilities . . . . . . . . . . . . 10 6.4. Decapsulating Node Responsibilities . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8.1. Post-Stack MNA Header First Nibble . . . . . . . . . . . 10 8.2. In-Stack Network Action Opcodes . . . . . . . . . . . . . 10 8.3. Post-Stack MNA Header Types Registry . . . . . . . . . . 11 8.4. Post-Stack Network Action Opcodes . . . . . . . . . . . . 12 9. Appendix A: Examples . . . . . . . . . . . . . . . . . . . . 12 9.1. Examples of Post-Stack MNA Encoding . . . . . . . . . . . 12 9.1.1. NAS that only Indicates Post-Stack MNA . . . . . . . 12 Rajamanickam, et al. Expires 21 September 2025 [Page 2] Internet-Draft Post-Stack MNA Solution March 2025 9.1.2. NAS that Indicates Post-Stack MNA Header Offset . . . 13 9.1.3. Post-Stack Network Action with Two Opcodes . . . . . 14 9.1.4. Post-Stack Network Action with two Different Scopes . . . . . . . . . . . . . . . . . . . . . . . 15 9.2. In-Stack and Post-Stack Network Actions . . . . . . . . . 16 9.2.1. NAS with In-Stack and Post-Stack NAs . . . . . . . . 16 9.2.2. NASes with Different In-Stack and Post-Stack Scopes . . . . . . . . . . . . . . . . . . . . . . . 17 9.2.3. Network Action Processing Order . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 10.1. Normative References . . . . . . . . . . . . . . . . . . 18 10.2. Informative References . . . . . . . . . . . . . . . . . 20 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 1. Introduction [RFC3032] defines the encoding of the MPLS label stack, the basic structure used to define a forwarding path. Forthcoming applications require MPLS packets to perform special network actions and carry optional Ancillary Data (AD) that can affect the packet forwarding decision or trigger Operations, Administration, and Maintenance (OAM) logging, for example. AD can be used to carry additional information, such as for In Situ OAM (IOAM) as described in [I-D.ietf-mpls-mna-usecases]. User-defined network actions allow local actions to be defined. In some cases, more AD may be required to be carried in the MPLS header, so these kinds of network actions and their AD are encoded after the Bottom of Stack (BOS). This AD is called Post-Stack Data. This document defines the Post-Stack MPLS Network Action (MNA) solution for carrying Network Actions and Ancillary Data after the MPLS label stack. It is based on the In-Stack MNA solution defined in [I-D.ietf-mpls-mna-hdr]. This solution document addresses the Post-Stack network action and Post-Stack data specific requirements found in [I-D.ietf-mpls-mna-requirements]. This document follows the architectural framework for the MPLS Network Actions (MNA) technologies specified in [I-D.ietf-mpls-mna-fwk]. 2. Conventions Used in This Document 2.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Rajamanickam, et al. Expires 21 September 2025 [Page 3] Internet-Draft Post-Stack MNA Solution March 2025 2.2. Abbreviations The terminology defined in [I-D.ietf-mpls-mna-fwk] and [I-D.ietf-mpls-mna-requirements] are used in this document. +============+=================+==================================+ |Abbreviation|Meaning | Reference | +============+=================+==================================+ |AD |Ancillary Data | [I-D.ietf-mpls-mna-requirements] | +------------+-----------------+----------------------------------+ |bSPL |Base Special | [RFC9017] | | |Purpose Label | | +------------+-----------------+----------------------------------+ |BOS |Bottom Of Stack | [RFC3032] | +------------+-----------------+----------------------------------+ |HBH |Hop-By-Hop Scope | [I-D.ietf-mpls-mna-fwk] | +------------+-----------------+----------------------------------+ |I2E |Ingress-To-Egress| [I-D.ietf-mpls-mna-fwk] | | |Scope | | +------------+-----------------+----------------------------------+ |IHS |I2E, HBH, or | [I-D.ietf-mpls-mna-hdr] | | |Select Scope | | +------------+-----------------+----------------------------------+ |ISD |In-Stack Data | [I-D.ietf-mpls-mna-requirements] | +------------+-----------------+----------------------------------+ |LSE |Label Stack Entry| [RFC3032] | +------------+-----------------+----------------------------------+ |MNA |MPLS Network | [I-D.ietf-mpls-mna-fwk] | | |Actions | | +------------+-----------------+----------------------------------+ |NAI |Network Action | [I-D.ietf-mpls-mna-requirements] | | |Indicator | | +------------+-----------------+----------------------------------+ |NAL |Network Action | [I-D.ietf-mpls-mna-hdr] | | |Length | | +------------+-----------------+----------------------------------+ |NAS |Network Action | [I-D.ietf-mpls-mna-fwk] | | |Sub-Stack | | +------------+-----------------+----------------------------------+ |NASL |Network Action | [I-D.ietf-mpls-mna-hdr] | | |Sub-Stack Length | | +------------+-----------------+----------------------------------+ |OAM |Operations, | [RFC6291] | | |Administration, | | | |and Maintenance | | +------------+-----------------+----------------------------------+ |P |Post-Stack MNA | This document | | |Indicator Bit | | Rajamanickam, et al. Expires 21 September 2025 [Page 4] Internet-Draft Post-Stack MNA Solution March 2025 +------------+-----------------+----------------------------------+ |PSD |Post-Stack Data | [I-D.ietf-mpls-mna-requirements] | | | | and [I-D.ietf-mpls-mna-fwk] | +------------+-----------------+----------------------------------+ |PS-MNA-OP |Post-Stack MPLS | This document | | |Network Action | | | |Opcode | | +------------+-----------------+----------------------------------+ |TC |Traffic Class | [RFC5462] | +------------+-----------------+----------------------------------+ |TTL |Time To Live | [RFC3032] | +------------+-----------------+----------------------------------+ Table 1: Abbreviations 3. Overview A flag in the In-Stack NAS header [I-D.ietf-mpls-mna-hdr] indicates the presence of the Post-Stack MNA in the packet. The Post-Stack MNA is encoded after the MPLS Label Stack (BOS), either immediately after the BOS (i.e., start offset of 0) or after any other Post-Stack headers that follow the BOS (i.e., start offset of non-zero). The Post-Stack MNA solution contains two main parts: * Post-Stack MNA Indicator in In-Stack MNA Sub-Stack * Post-Stack MNA Encoding 3.1. Post-Stack MNA Indicator in In-Stack MNA Sub-Stack A reserved bit (21st bit from the left in LSE Format B [I-D.ietf-mpls-mna-hdr]) in the In-Stack MNA Sub-Stack described in [I-D.ietf-mpls-mna-hdr] is used to indicate the presence of the Post- Stack MNA in the packet after the BOS. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode | Data |P|IHS|S|U| NASL | NAL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Post-Stack MNA Indicator in In-Stack MNA Sub-Stack The following are the flags applicable to Post-Stack MNA encoding purposes as defined in [I-D.ietf-mpls-mna-hdr]. Rajamanickam, et al. Expires 21 September 2025 [Page 5] Internet-Draft Post-Stack MNA Solution March 2025 * P (1 Bit): Indicates the presence of the Post-Stack MNA in the packet. * IHS (2 Bit): Indicates the combined scope of the In-Stack and the Post-Stack Network Actions. Each scope with P bit set will have its corresponding Post-Stack MNA Header sub-stack. * U (1 Bit): Indicates the combined Unknown Action Handling of the In-Stack and the Post-Stack Network Actions. 3.2. Post-Stack MNA Encoding The Post-Stack Network Action and its Ancillary Data are encoded after the MPLS Label Stack (BOS). The Post-Stack Network Action may carry multiple Post-Stack Network Actions and their corresponding Ancillary Data. This consist of two main parts: * Post-Stack MNA Header * Post-Stack Network Action Encoding 3.2.1. Post-Stack MNA Header This header is the top-level header for all the Post-Stack Network Actions that are encoded. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Post-Stack MNA Header * NNNN (4 bits): This first nibble identifies the start of the Post- Stack MNA Header [I-D.ietf-mpls-1stnibble]. A new value (value TBA1) is assigned by IANA. Editor's note: Generic Associated Channel (0001b) or CW (0000b) can be used. * Version (4 bits): This is Post-Stack MNA Header version. The initial version will be 0. * PS-HDR-LEN (8 bits): Post-Stack MNA Header Total Length in 4-octet units. This excludes the Post-Stack MNA Header. Rajamanickam, et al. Expires 21 September 2025 [Page 6] Internet-Draft Post-Stack MNA Solution March 2025 * TYPE (16 bits): Type is set to POST-STACK-HDR-MNA. The type value is an IANA allocated value of 1. 3.2.2. Post-Stack Network Action Encoding This header encodes a single Post-Stack Network Action. Using this scheme, multiple Post-Stack Network Action and its corresponding Ancillary data can be encoded. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP |R|R| PS-NAL | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Post-Stack Network Action Encoding * PS-MNA-OP (7 bits): Post-Stack Network Action Opcode. Opcode "0" is reserved and other opcodes will be assigned by IANA accordingly. * R (2 bits): Reserved bits. * PS-NAL (7 bits): Post-Stack Network Action Length in 4-octet units. This excludes the first 4-octets starting PS-MNA-OP. * POST-STACK DATA (16 bits): Post-Stack Data associated with the Post-Stack Network Action. 4. In-Stack Special Network Action Opcodes 4.1. In-Stack Network Action Opcode for Post-Stack MNA Header Offset Opcode: TBA2 Purpose: This opcode carries the start offset of the Post-Stack MNA Header from BOS. LSE Format: B (defined in [I-D.ietf-mpls-mna-hdr]) Data: The data value of the LSE contains the offset from the MPLS BOS in units of 4 octets. This allows the Generic Control Word (0000b) [RFC4385] and G-ACh (0001b) [RFC5586] fields to be placed immediately after the BOS. In the absence of this opcode, the Post-Stack MNA Header is encoded immediately after the MPLS BOS. A data value of 1 indicates that the Post-Stack MNA Header starts 4 octets after the BOS. Rajamanickam, et al. Expires 21 September 2025 [Page 7] Internet-Draft Post-Stack MNA Solution March 2025 Scope: This opcode can be used with any scope. 4.2. In-Stack Network Action Opcode for Post-Stack MNA Depth Offset Opcode: TBA3 Purpose: This opcode carries the depth of the Post-Stack MNA offset from BOS. LSE Format: B or C (defined in [I-D.ietf-mpls-mna-hdr]) Data: The data value of the LSE contains the offset from the MPLS BOS in units of 4 octets. A data value of 5 indicates that the Post- Stack MNA ends 20 octets after the BOS. Scope: This opcode can be used with any scope. 5. Procedure 5.1. Processing Rules for P Bit The P bit MUST be set to 1 in In-Stack Network Action Sub-Stack when Post-Stack MNA is added in the packet. By default, the Post-Stack MNA Header starts immediately after the BOS. The offset for the Post-Stack MNA Header that does not start immediately after the BOS is indicated using the Post-Stack MNA Header Offset Opcode TBA2. The P bit MUST be set to 1 when the network action with opcode TBA2 is added to the In-Stack Network Action Sub-Stack. The node that recognizes the network action with Opcode TBA2 MUST process the packet according to the U flag if the P bit is not set. The P bit MUST be set to 1 when the network action with opcode TBA3 is added to the In-Stack Network Action Sub-Stack. The node that recognizes the network action with Opcode TBA3 MUST process the packet according to the U flag if the P bit is not set. The node that supports the P bit will process the Post-Stack Network Actions in the Post-Stack MNA as defined in this document. Conversely, the node that does not support the P bit will skip processing the Post-Stack MNA altogether. Rajamanickam, et al. Expires 21 September 2025 [Page 8] Internet-Draft Post-Stack MNA Solution March 2025 5.2. Network Action Processing Order The Post-Stack Network Actions are processed in the same order they are encoded after the BOS. By default, they are processed after the In-Stack Network Actions in the Network Action Sub-Stack. However, Post-Stack Network Action Opcodes for applications (e.g., for IOAM application, to be defined in future) can be added in the In-Stack Network Action Sub-Stack to process Post-Stack Network Actions in a certain order with respect to the Opcodes in the In-Stack Network Action Sub-Stack. 5.3. Node Capability Signaling The ingress node that is adding a Post-Stack MNA MUST ensure that the egress node is capable of MNA and can remove the Post-Stack MNA from the packet. * Each participating node MUST signal the network actions that it supports. * Each participating node MUST signal its "Readable Label Depth including Post-Stack MNA" that can be encoded. The above capability signaling will be added in appropriate protocols. Signaling details are outside the scope of this document. 6. Nodes Processing Post-Stack Network Actions This section defines the specific responsibilities for nodes along an MPLS path for processing Post-Stack Network Actions. 6.1. Encapsulating Node Responsibilities The encapsulating node MAY add Post-Stack MNA to the packet in accordance with its policies, the placement restrictions, and the limitations. The encapsulating node MUST NOT add a Post-Stack MNA to the packet if the decapsulation node does not support Post-Stack MNA. If the encapsulating node is also a transit node, then it MUST also respect transit node responsibilities. 6.2. Transit Node Responsibilities A transit node MAY modify the Ancillary Data in the Post-Stack MNA. Rajamanickam, et al. Expires 21 September 2025 [Page 9] Internet-Draft Post-Stack MNA Solution March 2025 A transit node MUST respect the Unknown Action Handling value encoded in the NAS. A node that removes the last copy of a NAS that has the P bit set MUST remove all Post-Stack MNAs. 6.3. Penultimate Node Responsibilities In addition to the transit node responsibilities above, the penultimate node MUST NOT remove the last copy of an HBH or I2E NAS when it is exposed after removing the forwarding (transport) label. This allows the egress node to process the NAS. 6.4. Decapsulating Node Responsibilities The decapsulating node MUST remove any Post-Stack MNA it receives. 7. Security Considerations The security considerations in [RFC3032], [I-D.ietf-mpls-mna-fwk], and [I-D.ietf-mpls-mna-hdr] also apply to this document. 8. IANA Considerations 8.1. Post-Stack MNA Header First Nibble This document requests that IANA allocate a value (TBA1) for the Post-Stack MNA Header Nibble (NNNN) from the registry "Post-Stack First Nibble" created by [I-D.ietf-mpls-1stnibble] to indicate the start of the Post-Stack MNA Header. +=======+====================================+===============+ | Value | Description | Reference | +=======+====================================+===============+ | TBA1 | Post-Stack MNA Header First Nibble | This document | +-------+------------------------------------+---------------+ Table 2: Post-Stack First Nibble Registry 8.2. In-Stack Network Action Opcodes The In-Stack Network Action Opcodes for In-Stack Network Action Opcode registry (to be created by in [[I-D.ietf-mpls-mna-hdr]]) are defined in the document as follows. Rajamanickam, et al. Expires 21 September 2025 [Page 10] Internet-Draft Post-Stack MNA Solution March 2025 +========+==========================================+===============+ | Opcode | Description | Reference | +========+==========================================+===============+ | TBA2 | Offset of Start of Post-Stack MNA Header | This | | | | document | +--------+------------------------------------------+---------------+ | TBA3 | Offset of Depth of Post-Stack MNA | This | | | | document | +--------+------------------------------------------+---------------+ Table 3: In-Stack Network Action Flags With Ancillary Data Registry 8.3. Post-Stack MNA Header Types Registry This document requests that IANA create a new registry with the name "Post-Stack MNA Header Types". The registration procedure for this registry is "IETF Review". The fields are "Type" (integer), "Description" (string), and "Reference" (string). Type is an integer 0-65535. The assignments for this registry are: +=============+==============================+===============+ | Type | Description | Reference | +=============+==============================+===============+ | 0 | Reserved, not to be assigned | This document | +-------------+------------------------------+---------------+ | 1-65520 | IETF Review | This document | +-------------+------------------------------+---------------+ | 65521-65524 | Experimental Use | This document | +-------------+------------------------------+---------------+ | 65525-65535 | Private Use | This document | +-------------+------------------------------+---------------+ Table 4: Post-Stack MNA Header Types Registry The initial assignments for this registry are: +======+====================+===============+ | Type | Description | Reference | +======+====================+===============+ | 1 | POST-STACK-HDR-MNA | This document | +------+--------------------+---------------+ Table 5: Post-Stack MNA Header Types Rajamanickam, et al. Expires 21 September 2025 [Page 11] Internet-Draft Post-Stack MNA Solution March 2025 8.4. Post-Stack Network Action Opcodes This document requests that IANA create a new registry with the name "Post-Stack Network Action Opcodes". The registration procedure for this registry is "IETF Review". The fields are "Opcode" (integer), "Description" (string), and "Reference" (string). Opcode is an integer 0-127. The initial assignments for this registry are: +=========+==============================+===============+ | Opcode | Description | Reference | +=========+==============================+===============+ | 0 | Reserved, not to be assigned | This document | +---------+------------------------------+---------------+ | 1-110 | IETF Review | This document | +---------+------------------------------+---------------+ | 111-114 | Experimental Use | This document | +---------+------------------------------+---------------+ | 115-126 | Private Use | This document | +---------+------------------------------+---------------+ Table 6: Post-Stack Network Action Opcodes Registry 9. Appendix A: Examples 9.1. Examples of Post-Stack MNA Encoding 9.1.1. NAS that only Indicates Post-Stack MNA Rajamanickam, et al. Expires 21 September 2025 [Page 12] Internet-Draft Post-Stack MNA Solution March 2025 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opcode=2=NOOP| 0 |1|IHS|S|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |1| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP |R|R| PS-NAL=0 | PS ANCILLARY DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Payload ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: NAS that only indicates Post-Stack MNA In some cases, the NAS may encode only the presence of Post-Stack MNA. The Post-Stack MNA Header starts immediately after the BOS. 9.1.2. NAS that Indicates Post-Stack MNA Header Offset Rajamanickam, et al. Expires 21 September 2025 [Page 13] Internet-Draft Post-Stack MNA Solution March 2025 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=TBA2 | Post-Stack Offset = 2 |1|IHS|S|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |1| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP |R|R| PS-NAL=0 | PS ANCILLARY DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Payload ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: NAS Indicates Post-Stack MNA Header Offset The NAS may encode the start offset for the Post-Stack MNA Header with a non-zero value, for example, when it is after other header such as GACH or CW header. In this example, the PSH starts at offset of 8 bytes after the BoS. 9.1.3. Post-Stack Network Action with Two Opcodes Rajamanickam, et al. Expires 21 September 2025 [Page 14] Internet-Draft Post-Stack MNA Solution March 2025 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opcode=2=NOOP| 0 |1|IHS|1|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=3 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP=2|R|R| PS-NAL=0 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP=3|R|R| PS-NAL=1 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Optional Payload + Padding | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Post-Stack NA with Two Opcodes This is an example, Post-Stack MNA encodes two different Post-Stack Network Actions. Details: PS-HDR-LEN=3: This is the Total Length of Post-Stack MNA. PS-MNA-OP=2: Post-Stack MNA Opcode "2". PS-NAL=0: Post-Stack Network Action does not contain any additional data. PS-MNA-OP=3: Post-Stack MNA Opcode "3". PS-NAL=1: Post-Stack Network Action contains 1 additional 4-octet Ancillary data. 9.1.4. Post-Stack Network Action with two Different Scopes Rajamanickam, et al. Expires 21 September 2025 [Page 15] Internet-Draft Post-Stack MNA Solution March 2025 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opcode=2=NOOP| 0 |1|HBH|0|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=TBA2 | Post-Stack Offset = 2 |1|I2E|1|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP=2|R|R| PS-NAL=0 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=2 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP=3|R|R| PS-NAL=1 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Optional Payload + Padding | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: Post-Stack NA with two Different Scopes This is an example of Post-Stack MNA encoding, that encode two different different scoped Post-Stack Network Actions. The first scope is Hop-By-Hop and the second scope is Ingress-To-Egress scoped Post-Stack Network Action. Details: The offset of the Hop-By-Hop scoped Post-Stack Network Action 0. Opcode TBA2 carries the offset of the Ingress-To-Egress scoped Post-Stack Network Action. The data is "2," i.e., the Post-Stack MNA Header starts 8 bytes after the MPLS Bottom of Stack. 9.2. In-Stack and Post-Stack Network Actions 9.2.1. NAS with In-Stack and Post-Stack NAs Rajamanickam, et al. Expires 21 September 2025 [Page 16] Internet-Draft Post-Stack MNA Solution March 2025 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Flag-Based NAIs |1|IHS|S|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |1| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP |R|R| PS-NAL=0 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Payload ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: NAS with In-Stack and Post-Stack NAs In some cases, the NAS may encode In-Stack NAs and indicate the presence of Post-Stack MNA Header. The IHS field indicates the scope of both the In-Stack and Post-Stack NAs. 9.2.2. NASes with Different In-Stack and Post-Stack Scopes 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Flag-Based NAIs |0|HBH|0|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opcode=2=NOOP| 0 |1|I2E|1|U| NASL=0|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PS-MNA-OP |R|R| PS-NAL=0 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Payload ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Rajamanickam, et al. Expires 21 September 2025 [Page 17] Internet-Draft Post-Stack MNA Solution March 2025 Figure 9: NASes with Different In-Stack and Post-Stack Scopes In some cases the label stack may need to carry In-Stack NAs with Hop-By-Hop scope and Post-Stack NAs with I2E scope. In this case, there will be two NASes in the label stack. In this case, the first NAS will encode the In-Stack NA with the Hop-By-Hop scope and the second NAS will encode the presence of I2E scoped Post-Stack NAs. 9.2.3. Network Action Processing Order The Post-Stack NA opcode can be added to interleave Post-Stack network actions with In-Stack network actions. The following example shows how to process the Post-Stack NA before the In-Stack NA. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=8 | Ancillary Data |1|IHS|0|U| NASL=3|NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Flag-Based NAIs |0|U| NAIs |NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opcode=IOAMPS| Post-Stack Offset=1 |0|U|PS-NAI |NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=7 | Ancillary Data |1|U| AD |NAL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |N N N N|Version| PS-HDR-LEN=1 | TYPE = POST-STACK-HDR-MNA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PS-OP=IOAMPS |R|R| PS-NAL=0 | POST-STACK DATA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: Post-Stack and In-Stack NA Processing Order In this example, opcode 8 is processed first, followed by the Flag- Based NAIs, then the Post-Stack NA Opcode IOAMPS (which has an offset of 1 word, i.e., 4 bytes), and finally opcode 7. 10. References 10.1. Normative References [I-D.ietf-mpls-mna-fwk] Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS Network Actions (MNA) Framework", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-fwk-15, 27 December 2024, . Rajamanickam, et al. Expires 21 September 2025 [Page 18] Internet-Draft Post-Stack MNA Solution March 2025 [I-D.ietf-mpls-mna-requirements] Bocci, M., Bryant, S., and J. Drake, "Requirements for Solutions that Support MPLS Network Actions (MNA)", Work in Progress, Internet-Draft, draft-ietf-mpls-mna- requirements-16, 30 May 2024, . [I-D.ietf-mpls-mna-hdr] Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K. Kompella, "MPLS Network Action (MNA) Sub-Stack Solution", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr- 12, 3 March 2025, . [I-D.ietf-mpls-1stnibble] Kompella, K., Bryant, S., Bocci, M., Mirsky, G., Andersson, L., and J. Dong, "IANA Registry and Processing Recommendations for the First Nibble Following a Label Stack", Work in Progress, Internet-Draft, draft-ietf-mpls- 1stnibble-13, 5 December 2024, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [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, . [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, . [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, June 2009, . Rajamanickam, et al. Expires 21 September 2025 [Page 19] Internet-Draft Post-Stack MNA Solution March 2025 [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9017] Andersson, L., Kompella, K., and A. Farrel, "Special- Purpose Label Terminology", RFC 9017, DOI 10.17487/RFC9017, April 2021, . 10.2. Informative References [I-D.ietf-mpls-mna-usecases] Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use Cases for MPLS Network Action Indicators and MPLS Ancillary Data", Work in Progress, Internet-Draft, draft- ietf-mpls-mna-usecases-15, 23 September 2024, . 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 Rajamanickam, et al. Expires 21 September 2025 [Page 20] Internet-Draft Post-Stack MNA Solution March 2025 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 Rajamanickam, et al. Expires 21 September 2025 [Page 21]