Post-Stack MPLS Network Action (MNA) Header Specification
draft-ietf-mpls-mna-ps-hdr-12
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Authors | Jaganbabu Rajamanickam , Rakesh Gandhi , Royi Zigler , Jie Dong , Jisu Bhattacharya | ||
| Last updated | 2026-07-30 (Latest revision 2026-07-29) | ||
| Replaces | draft-jags-mpls-ps-mna-hdr | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
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by Ted Lemon
Ready w/issues
RTGDIR IETF Last Call Review due 2026-06-09
Incomplete
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Associated WG milestone |
|
||
| Document shepherd | Adrian Farrel | ||
| Shepherd write-up | Show Last changed 2026-04-14 | ||
| IESG | IESG state | IESG Evaluation | |
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Has a DISCUSS. Has enough positions to pass once DISCUSS positions are resolved. |
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| Responsible AD | Jim Guichard | ||
| Send notices to | adrian@olddog.co.uk | ||
| IANA | IANA review state | Version Changed - Review Needed |
draft-ietf-mpls-mna-ps-hdr-12
MPLS Working Group J. Rajamanickam, Ed.
Internet-Draft R. Gandhi, Ed.
Updates: 9994 (if approved) Cisco Systems, Inc.
Intended status: Standards Track R. Zigler
Expires: 31 January 2027 Broadcom
J. Dong
Huawei Technologies
J. Bhattacharya
Cisco Systems, Inc.
30 July 2026
Post-Stack MPLS Network Action (MNA) Header Specification
draft-ietf-mpls-mna-ps-hdr-12
Abstract
This document specifies the Post-Stack MPLS Network Action (MNA)
Header encoding and procedures for carrying Network Action encodings
and Ancillary Data after the MPLS label stack, based on the MNA Sub-
Stack including In-Stack Network Actions and Data specified in RFC
9994. MPLS Network Actions can be used to influence packet
forwarding decisions, carry additional Operations, Administration,
and Maintenance information in the MPLS packet, or perform user-
defined operations. This document follows the framework specified in
RFC 9789.
This document updates RFC 9994: the "Network Action Opcodes" registry
fields, the Post-Stack MNA applicability of the opcodes, MNA scope,
and Unknown action handling.
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 31 January 2027.
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Copyright Notice
Copyright (c) 2026 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 . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. PSMH Presence Bit Carried in In-Stack Network Action
Sub-Stack . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. PSMH Encoding . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. Post-Stack MPLS Base Header . . . . . . . . . . . . . 6
3.2.2. Post-Stack Network Actions Encoding . . . . . . . . . 7
3.2.3. Example Encoding of an MPLS Packet with PSMH . . . . 8
4. In-Stack Network Action Special Opcodes . . . . . . . . . . . 10
4.1. Opcode for PSMH Start Offset . . . . . . . . . . . . . . 10
4.2. Opcode for PSMH End Offset . . . . . . . . . . . . . . . 10
5. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Processing Rules for P Bit . . . . . . . . . . . . . . . 11
5.2. Network Action Processing Order . . . . . . . . . . . . . 12
5.3. Node Capability Signaling . . . . . . . . . . . . . . . . 12
5.4. Post-Stack MNA and BIER Header . . . . . . . . . . . . . 12
6. Processing the Network Action Sub-Stack and Post-Stack
Header . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Encapsulating Node Responsibilities . . . . . . . . . . . 13
6.2. Transit Node Responsibilities . . . . . . . . . . . . . . 13
6.3. Penultimate Node Responsibilities . . . . . . . . . . . . 13
6.4. Egress Node Responsibilities . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Operational Considerations . . . . . . . . . . . . . . . . . 14
8.1. Manageability Considerations . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9.1. First Nibble for Post-Stack MPLS Header . . . . . . . . . 15
9.2. Post-Stack MPLS Header Types Registry . . . . . . . . . . 15
9.3. Network Action Opcodes . . . . . . . . . . . . . . . . . 16
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 19
A.1. Examples of PSMH Encoding . . . . . . . . . . . . . . . . 19
A.1.1. NAS that only indicates PSMH . . . . . . . . . . . . 19
A.1.2. NAS that Indicates PSMH Start Offset . . . . . . . . 20
A.1.3. Post-Stack Network Actions with Two Opcodes . . . . . 21
A.1.4. Post-Stack Network Actions with Two Different
Scopes . . . . . . . . . . . . . . . . . . . . . . . 22
A.2. Examples of In-Stack and Post-Stack Network Actions . . . 24
A.2.1. NAS with In-Stack and Post-Stack Network Actions . . 24
A.2.2. NASes with Different In-Stack and Post-Stack
Scopes . . . . . . . . . . . . . . . . . . . . . . . 25
A.2.3. NAS with a BIER Header . . . . . . . . . . . . . . . 25
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 26
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
[RFC3032] defines the encoding of the MPLS label stack, the basic
structure used to define a forwarding path. There are applications
that 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, as described in [RFC9791]. AD can be used
to carry additional information for network slice purposes, as
described in [RFC9791].
In some cases, more AD may be required than can 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 the Post-Stack (PS) MNA.
The requirements for Post-Stack Network Actions and Post-Stack Data
(PSD) are described in [RFC9613].
This document specifies the Post-Stack MPLS Network Action (MNA)
header encoding and procedures for carrying Network Action encodings
and AD after the MPLS label stack. The specification is based on the
MNA Sub-Stack, including In-Stack Network Actions and Data, specified
in [RFC9994]. This document follows the framework specified in
[RFC9789].
This document updates [RFC9994]: the "Network Action Opcodes"
registry fields, the Post-Stack MNA applicability of the opcodes, MNA
scope, and Unknown action handling.
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2. Conventions Used in This Document
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Abbreviations
The terminology defined in [RFC9613] is used in this document.
+==============+=================================+===============+
| Abbreviation | Meaning | Reference |
+==============+=================================+===============+
| AD | Ancillary Data | [RFC9613] |
+--------------+---------------------------------+---------------+
| bSPL | Base Special-Purpose Label | [RFC9017] |
+--------------+---------------------------------+---------------+
| BIER | Bit Index Explicit Replication | [RFC8296] |
+--------------+---------------------------------+---------------+
| BoS | Bottom of Stack | [RFC9789] |
+--------------+---------------------------------+---------------+
| HbH | Hop-by-Hop | [RFC9789] |
+--------------+---------------------------------+---------------+
| I2E | Ingress to Egress | [RFC9789] |
+--------------+---------------------------------+---------------+
| IHS | I2E, HbH, or Select | [RFC9994] |
+--------------+---------------------------------+---------------+
| ISD | In-Stack Data | [RFC9613] |
+--------------+---------------------------------+---------------+
| LSE | Label Stack Entry | [RFC9789] |
+--------------+---------------------------------+---------------+
| MNA | MPLS Network Action | [RFC9789] |
+--------------+---------------------------------+---------------+
| NAI | Network Action Indicator | [RFC9613] |
+--------------+---------------------------------+---------------+
| NAL | Network Action Length | [RFC9994] |
+--------------+---------------------------------+---------------+
| NAS | Network Action Sub-Stack | [RFC9789] |
+--------------+---------------------------------+---------------+
| NASL | Network Action Sub-Stack Length | [RFC9994] |
+--------------+---------------------------------+---------------+
| OAM | Operations, Administration, and | [RFC6291] |
| | Maintenance | |
+--------------+---------------------------------+---------------+
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| PFN | Post-Stack First Nibble | [RFC9790] |
+--------------+---------------------------------+---------------+
| P bit | Post-Stack MPLS Header Presence | This document |
| | Bit | |
+--------------+---------------------------------+---------------+
| PS | Post-Stack | This document |
+--------------+---------------------------------+---------------+
| PSD | Post-Stack Data | [RFC9613] and |
| | | [RFC9789] |
+--------------+---------------------------------+---------------+
| PSMH | Post-Stack MPLS Header | This document |
+--------------+---------------------------------+---------------+
| PSNA | Post-Stack Network Action | This document |
+--------------+---------------------------------+---------------+
| TC | Traffic Class | [RFC5462] |
+--------------+---------------------------------+---------------+
| TTL | Time to Live | [RFC3032] |
+--------------+---------------------------------+---------------+
Table 1: Abbreviations
3. Overview
Two main parts are specified to support Post-Stack MNA:
* The Post-Stack MPLS Header (PSMH) Presence Bit Carried in In-Stack
MNA Sub-Stack.
* The PSMH encoding that includes a Post-Stack MPLS Base Header and
one or more Post-Stack Network Actions and their AD.
Note that the PSMH can be encoded for use cases other than the PS
MNA. However, this document only describes the procedure related to
the Post-Stack MNA.
3.1. PSMH Presence Bit Carried in In-Stack Network Action Sub-Stack
The bit at position 20 in LSE Format B, specified as the R (Reserved)
bit in Section 4.2 of [RFC9994], in the In-Stack Network Action Sub-
Stack (NAS) is defined as the P bit in this document to indicate the
presence of the PSMH 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 | 13-bit Data (Format B) |P|IHS|S| NASL |U| NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 1: PSMH Presence Bit Carried in In-Stack MNA Sub-Stack
The following fields are carried in the Format B LSE in an NAS as
defined in [RFC9994] and shown in Figure 1.
* S (1 bit): The BoS [RFC3032].
* NASL (4 bits): The Network Action Sub-Stack Length.
* NAL (3 bits): The Network Action Length.
* Opcode (7 bits): The Opcode encoded as defined in [RFC9994].
* Data (13 bits): The associated AD encoded as defined in [RFC9994].
This document updates [RFC9994] for the following fields carried in a
Format B LSE in an NAS:
* IHS (2 bits): The scope of all the NAIs encoded in the NAS, as
well as in the corresponding PSMH.
* U (1 bit): Indicates the combined Unknown Action Handling of the
In-Stack and the Post-Stack Network Actions.
3.2. PSMH Encoding
The PSMH is encoded after the LSE for which the BoS bit is set,
either immediately after the BoS (i.e., start offset of 0) or after
any other Post-Stack headers that follow the BoS (i.e., a non-zero
start offset), as described in Section 4.
The PSMH consists of two main parts:
* Post-Stack MPLS Base Header
* Encoding for one or more Post-Stack Network Actions (PSNAs) and
their AD
3.2.1. Post-Stack MPLS Base Header
Post-Stack MPLS Base Header is defined as shown in Figure 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PFN |Reserve| PSMH-Len | Post-Stack MPLS Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 2: Post-Stack MPLS Base Header
* PFN (4 bits): The Post-Stack First Nibble (PFN) [RFC9790]
identifies the start of the PSMH. The PFN is set to 0x0 for the
PSMH.
* Reserve (4 bits): Reserved bits. MUST be set to zero on
transmission and ignored upon receipt.
* PSMH-Len (8 bits): The PSMH total length in 4-octet units. The
length excludes the 4-octet Post-Stack MPLS Base Header.
* Type (16 bits): Post-Stack MPLS Header Type. See Section 9.2.
Note that other types of PSMHs can be defined in the future
(besides the "MNA Post-Stack Header" defined in this document) and
are outside the scope of this document.
3.2.1.1. Post-Stack MPLS Base Header for MNA
For PS MNA, the Post-Stack MPLS Base Header shown in Figure 2 is
added for each NAS in which the P bit is set. The Post-Stack MPLS
Header Type is set to 1 for "MNA Post-Stack Header" and the PSMH-Len
includes the encoding of the Post-Stack Network Actions.
If a node does not recognize the Post-Stack MPLS Header Type, the
packet is handled based on the setting of the U bit in the NAS.
PSMH-Len MUST be greater than 0, otherwise, the packet is recognized
as malformed and MUST be dropped regardless of the setting of the U
bit in the NAS.
If a node encounters unexpected PFN in a PSMH, the packet is
recognized as malformed and MUST be dropped regardless of the setting
of the U bit in the NAS.
3.2.2. Post-Stack Network Actions Encoding
The format shown in Figure 3 encodes a single Post-Stack Network
Action. By repeating this format, multiple Post-Stack Network
Actions and their corresponding AD 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Continued Post-Stack Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 3: Post-Stack Network Action Encoding
* MNA-PS-OP (7 bits): Post-Stack Network Action Opcode.
* R (2 bits): Reserved bits. MUST be set to zero on transmission
and ignored upon receipt.
* PS-NAL (7 bits): Post-Stack Network Action Length in 4-octet
units. This excludes the first 4 octets starting with MNA-PS-OP.
* Post-Stack Data (16 bits): PSD associated with the Post-Stack
Network Action.
* Continued Post-Stack Data: Further PSD associated with the Post-
Stack Network Action, as indicated by the value of the PS-NAL.
The padding rules for PSD that do not fill a multiple of 4-octet
units are described in the document that defines the Network
Action, as indicated by the MNA-PS-OP value.
The sum of PS-NAL plus one for the 4-octet network action word for
all network actions encoded in a PSMH MUST equal to the PSMH-Len. If
not, the packet is recognized as malformed and MUST be dropped
regardless of the setting of the U bit in the NAS.
This document updates [RFC9994]: the "Network Action Opcodes"
registry fields and the Post-Stack MNA applicability of the opcodes
defined in [RFC9994] as follows. See Section 9.3.
* Value for MNA-PS-OP is assigned from the same registry shared by
Post-Stack and In-Stack network action opcodes.
* A document defining a new network action opcode MUST specify the
applicability as "In-Stack", "Post-Stack" or "In-Stack and Post-
Stack".
* The packets with opcode 127, defined in [RFC9994], when carried in
Post-Stack, MUST be dropped regardless of the setting of the U bit
in the NAS.
* In case of opcode 1 for Flag-Based NAIs Without AD, defined in
[RFC9994], when carried in Post-Stack, the same bit position of
the flags are mapped in ISD and PSD.
3.2.3. Example Encoding of an MPLS Packet with PSMH
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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
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
M | MNA Label (value 4) | TC |0| TTL | N
P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A
L | Opcode=2 | 0 |1|IHS|0| NASL=0|U|NAL=0| S
S +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
H ~ |0| ~
D +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R | |1| |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
| | 0x0 |Reserve| PSMH-Len | Type = MNA Post-Stack Header | B
P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
S | MNA-PS-OP |R|R| PS-NAL | Post-Stack Data | P
M +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ S
H ~ Continued Post-Stack Data ~ N
| ~ ~ A
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Example Encoding of an MPLS Packet with PSMH
An example encoding of an MPLS packet shown in Figure 4 consists of
the following two main parts:
* MPLS HDR: MPLS header includes an MPLS label stack and NAS.
* PSMH: Post-Stack MPLS Header includes the Post-Stack MPLS Base
Header and the Post-Stack Network Actions encoding.
The MPLS header includes the following field:
* NAS: Network Action Sub-Stack. MNA Label set to 4 [RFC9994]. The
P bit set to 1 to indicate the presence of the corresponding PSMH
in the packet. An MPLS packet may carry more than one NAS, not
shown in Figure 4.
The PSMH includes the following fields:
* B: The Post-Stack MPLS Base Header for the "MNA Post-Stack Header"
type.
* PSNA: Post-Stack Network Actions encoding. Applicable to the "MNA
Post-Stack Header" type. An MPLS packet may have more than one
Post-Stack Network Action; this is not shown in Figure 4.
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4. In-Stack Network Action Special Opcodes
4.1. Opcode for PSMH Start Offset
Opcode: TBA1
Purpose: This opcode carries the start offset of the PSMH from the
BoS.
LSE Format: B or C (defined in [RFC9994]).
Data: The data value of the LSE contains the offset from the BoS in
4-octet units. A data value of 1 indicates that the PSMH starts at 4
octets after the BoS.
Scope: This opcode can be used with any scope.
This opcode allows existing Post-Stack Headers [RFC9790], such as the
Pseudowire (PW) Control Word (0x0) [RFC4385] and Generic Associated
Channel (G-ACh) (0x1) [RFC5586], as well as any other PSH defined in
the future, to be placed after the BoS and before the PSMH.
A PSMH added in the packet follows the PSHs and MUST be added along
with opcode TBA1 in the NAS that specify the offset of the PSMH.
If the P bit is set in a given NAS and the PSMH Start Offset opcode
is absent, the PSMH is encoded immediately after the BoS in the
absence of other PSHs.
This opcode MUST be added in every NAS beyond the first NAS, when the
P bit is set in the NAS, to carry the offset of the corresponding
PSMH.
This opcode can be placed in an NAS to process the Post-Stack Network
Actions in a certain order with respect to the other Opcodes in the
NAS. This opcode can be used with offset value 0 to influence the
processing order in an NAS.
The offset value is set to 0 when the PSMH starts immediately after
the BoS.
4.2. Opcode for PSMH End Offset
Opcode: TBA2
Purpose: This opcode carries the offset of the end of the PSMH from
the BoS.
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LSE Format: B or C (defined in [RFC9994]).
Data: The data value of the LSE contains the offset from the BoS in
4-octet units. A data value of 5 indicates that the PSMH ends at 20
octets after the BoS.
Scope: This opcode can be used with any scope.
The offset of the end of the PSMH and the offset of the start of the
PSMH allow the NAS parser implementation to know the size of the PSMH
without having to parse the PSMH (e.g., for Readable Label Depth with
PSMH checks).
When the opcode TBA2 is added in an NAS, it MUST be added immediately
after the PSMH Start Offset opcode (value TBA1) when the opcode TBA1
is also present in the NAS.
The offset value in opcode TBA2 MUST be greater than the offset value
in opcode TBA1. Otherwise, the packet is recognized as malformed and
MUST be dropped regardless of the setting of the U bit in the NAS.
This opcode is optional and can be placed anywhere in an NAS and does
not affect the processing order of the network actions in the NAS and
the corresponding PSMH.
5. Procedure
5.1. Processing Rules for P Bit
The P bit MUST be set to 1 in an In-Stack Network Action Sub-Stack
when the corresponding PSMH is added in the packet.
By default, the PSMH starts immediately after the BoS. The offset of
the PSMH that does not start immediately after the BoS is indicated
using the PSMH Start Offset Opcode TBA1.
The P bit MUST be set to 1 when the network action with opcode TBA1
is added to the In-Stack Network Action Sub-Stack. The node that
recognizes the network action with opcode TBA1 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 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.
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A node that supports the P bit processes the Post-Stack Network
Actions in the PSMH as defined in this document. Conversely, a node
that does not support the P bit skips processing the PSMH 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.
5.3. Node Capability Signaling
* Each participating transit and egress node MUST signal the Post-
Stack Network Actions that it supports to the encapsulating node.
* Each participating transit and egress node MUST signal its
"Readable Label Depth including PSMH" that can be used by the
encapsulating node. Note that the "Readable Label Depth" defined
in [RFC9994] is extended in this document to include the length of
the PSMH.
The above capability signaling will be added in appropriate protocols
in the future. Signaling details are outside the scope of this
document.
5.4. Post-Stack MNA and BIER Header
[RFC8296] specifies the Bit Index Explicit Replication (BIER)
encapsulation for an MPLS network. The BIER header, defined in
Section 2 of [RFC8296], is used to replicate and forward multicast
packets to all their next hops by Bit-Forwarding Routers (BFRs).
[RFC9994] does not specify an encoding format to carry a NAS along
with the BIER header that is processed on a BFR. Since the PSMH uses
the NAS defined in [RFC9994], the processing of a PSMH on a BFR node
is outside the scope of this document.
6. Processing the Network Action Sub-Stack and Post-Stack Header
The processing of the Network Action Sub-Stack described in [RFC9994]
also applies to the procedures defined in this document. This
section defines the specific responsibilities for nodes along an MPLS
path for processing a PSMH.
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6.1. Encapsulating Node Responsibilities
The encapsulating node MAY add a PSMH to the packet. The location of
the header MAY be in accordance with local policy. The location may
also be subject to any placement restrictions inherent in the
implementation.
The encapsulating node MUST NOT add a PSMH to the packet if the
egress node does not support PSMH.
The encapsulating node MUST ensure that the packet with all PSMHs
added does not exceed the path MTU, as specified in Section 8 of
[RFC9994].
The encapsulating node MUST add the PSMH in the same order as the
corresponding NAS in the MPLS header.
6.2. Transit Node Responsibilities
A transit node within the scope of the corresponding NAS MAY modify
the Ancillary Data in the PSMH. Such modification MUST NOT change
the length of the PSMH.
A transit node MUST respect the Unknown Action Handling flag encoded
in the corresponding NAS when processing the PSMH.
A transit node that removes an NAS with the Select scope MUST also
remove the associated PSMH.
6.3. Penultimate Node Responsibilities
In addition to the transit node responsibilities above, the
penultimate node MUST NOT remove a Hop-by-Hop (HbH) or Ingress to
Egress (I2E) NAS [RFC9994] and the associated PSMH when the NAS is
exposed after removing the forwarding (transport) label. This allows
the egress node to receive and process the NAS and the associated
PSMH.
6.4. Egress Node Responsibilities
The egress node MUST remove the PSMHs from the packet when it removes
the NASes.
7. Security Considerations
The security considerations in [RFC3032], [RFC9789], and [RFC9994]
also apply to this document.
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System designers must be aware that information included in Post-
Stack AD may be transmitted "in the clear". Network actions that
require the exchange of sensitive data MUST be defined in such a way
that the data is encrypted in transit. Otherwise, sensitive data
MUST NOT be transmitted using these mechanisms.
8. Operational Considerations
The operational considerations in [RFC9994] also apply to this
document.
Performance and scale assessments are outside the scope of this
document; the authors of any future PS MNA application documents are
encouraged to address them.
The MPLS OAM packets, for example using G-ACh (with PFN 0x1)
[RFC5586], may be transmitted carrying MNA with PSMH for performing
network diagnostics. However, specification for this is outside the
scope of this document.
8.1. Manageability Considerations
A PS MNA implementation MAY collect the following counters:
* Packets with PSMH received
* Packets with PSMH dropped due to unknown actions
* Packets with PSMH skipped due to unknown actions
* Packets with PSMH dropped due to malformed PSMH
* Per-Post-Stack Network Action counters
Additionally, tracking both successful invocations and failures for
each specific Post-Stack Network Action is RECOMMENDED to provide
granular visibility. Nodes MAY generate rate-limited notifications
or alarms for significant operational events, such as sustained high
rates of PS MNA packet drops or frequent encounters of malformed
PSMH, to alert operators to potential issues. Comprehensive logging
of PS MNA processing details and outcomes can aid in network
diagnostics and post-mortem analysis.
9. IANA Considerations
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9.1. First Nibble for Post-Stack MPLS Header
This document requests that IANA add the following entry to the
"Post-Stack First Nibble" registry created by [RFC9790].
+==========+=======+========================+===============+
| Protocol | Value | Description | Reference |
+==========+=======+========================+===============+
| MPLS | 0x0 | Post-Stack MPLS Header | This document |
+----------+-------+------------------------+---------------+
Table 2: Post-Stack First Nibble Registry
9.2. Post-Stack MPLS Header Types Registry
This document requests that IANA create a new registry with the name
"Post-Stack MPLS Header Types" within the "MPLS Network Actions"
registry group. The registration procedures for this registry are
"IETF Review", "Experimental Use", and "Private Use". The fields are
"Type" (integer), "Description" (string), and "Reference" (string).
This registry is added under "MPLS Network Actions" because the
container is defined by an MNA document. Note that adding this
registry there makes it easy for discovering, but the Type space is
not MNA-specific, the document itself anticipates non-MNA PSMH types
whose codepoints would then be allocated from a registry added under
MNA.
The Registration Procedures for this registry are:
+=============+=========================+
| Range | Registration Procedures |
+=============+=========================+
| 1-65520 | IETF Review |
+-------------+-------------------------+
| 65521-65524 | Experimental Use |
+-------------+-------------------------+
| 65525-65535 | Private Use |
+-------------+-------------------------+
Table 3: Registration Procedures for
the Post-Stack MPLS Header Types
Registry
The initial assignments for this registry are:
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+======+=======================+===============+
| Type | Description | Reference |
+======+=======================+===============+
| 0 | Reserved | This document |
+------+-----------------------+---------------+
| 1 | MNA Post-Stack Header | This document |
+------+-----------------------+---------------+
Table 4: Post-Stack MPLS Header Types
9.3. Network Action Opcodes
IANA maintains the "Network Action Opcodes" registry that is created
by [RFC9994]. IANA is requested to perform two actions for this
registry:
1. Assign two code points for network actions defined in this
document.
2. Add a new column for Applicability with values to indicate
whether network action opcodes may be used as In-Stack only, Post-
Stack only, or In-Stack and Post-Stack. By default, the unassigned
values are applicable for In-Stack and Post-Stack network actions.
This table to be updated for the RFC-ietf-mpls-mna-nrp-selector-07
for [I-D.ietf-mpls-mna-nrp-selector].
The resulting entries in the registry are as follows:
+=======+============+=============+================================+
|Opcode |Description |Applicability|Reference |
+=======+============+=============+================================+
|0 |Reserved |Not |[RFC9994] |
| | |Applicable | |
+-------+------------+-------------+--------------------------------+
|1 |Flag-Based |In-Stack Only|[RFC9994] |
| |Network | | |
| |Action | | |
| |Indicators | | |
| |without AD | | |
+-------+------------+-------------+--------------------------------+
|2 |No operation|In-Stack and |[RFC9994] |
| |Opcode |Post-Stack | |
+-------+------------+-------------+--------------------------------+
|3 |13-bit NRP |In-Stack Only|[I-D.ietf-mpls-mna-nrp-selector]|
| |Selector | | |
+-------+------------+-------------+--------------------------------+
|4 |20-bit NRP |In-Stack Only|[I-D.ietf-mpls-mna-nrp-selector]|
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| |Selector | | |
+-------+------------+-------------+--------------------------------+
|5 |20-bit |In-Stack Only|[I-D.ietf-mpls-mna-nrp-selector]|
| |Entropy and | | |
| |NRP Selector| | |
+-------+------------+-------------+--------------------------------+
|6-110 |Unassigned |In-Stack and | |
| | |Post-Stack | |
+-------+------------+-------------+--------------------------------+
|111-114|Reserved for|In-Stack and |[RFC9994] |
| |Experimental|Post-Stack | |
| |Use | | |
+-------+------------+-------------+--------------------------------+
|115-126|Reserved for|In-Stack and |[RFC9994] |
| |Private Use |Post-Stack | |
+-------+------------+-------------+--------------------------------+
|TBA1 |Post-Stack |In-Stack Only|This document |
| |MPLS Header | | |
| |Start Offset| | |
+-------+------------+-------------+--------------------------------+
|TBA2 |Post-Stack |In-Stack Only|This document |
| |MPLS Header | | |
| |End Offset | | |
+-------+------------+-------------+--------------------------------+
|127 |Opcode Range|In-Stack and |[RFC9994] |
| |Extension |Post-Stack | |
| |Beyond 127 | | |
+-------+------------+-------------+--------------------------------+
Table 5: Network Action Opcodes
10. References
10.1. Normative References
[RFC9994] Rajamanickam, J., Ed., Gandhi, R., Ed., Zigler, R., Song,
H., and K. Kompella, "MPLS Network Action (MNA) Sub-Stack
Specification Including In-Stack Network Actions and
Data", RFC 9994, DOI 10.17487/RFC9994, June 2026,
<https://www.rfc-editor.org/info/rfc9994>.
[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>.
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[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>.
[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>.
[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>.
[RFC9789] Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions (MNAs) Framework", RFC 9789,
DOI 10.17487/RFC9789, July 2025,
<https://www.rfc-editor.org/info/rfc9789>.
[RFC9790] Kompella, K., Bryant, S., Bocci, M., Mirsky, G., Ed.,
Andersson, L., and J. Dong, "IANA Registry and Processing
Recommendations for the First Nibble Following a Label
Stack", RFC 9790, DOI 10.17487/RFC9790, July 2025,
<https://www.rfc-editor.org/info/rfc9790>.
10.2. Informative References
[I-D.ietf-mpls-mna-nrp-selector]
Li, T., Beeram, V. P., Drake, J., Saad, T., and I. Meilik,
"MPLS Network Actions for Network Resource Partition
Selector", Work in Progress, Internet-Draft, draft-ietf-
mpls-mna-nrp-selector-07, 11 June 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-nrp-selector-07>.
[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>.
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[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>.
[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>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC9613] Bocci, M., Ed., Bryant, S., and J. Drake, "Requirements
for Solutions that Support MPLS Network Actions (MNAs)",
RFC 9613, DOI 10.17487/RFC9613, August 2024,
<https://www.rfc-editor.org/info/rfc9613>.
[RFC9791] Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use
Cases for MPLS Network Action Indicators and Ancillary
Data", RFC 9791, DOI 10.17487/RFC9791, July 2025,
<https://www.rfc-editor.org/info/rfc9791>.
Appendix A. Examples
A.1. Examples of PSMH Encoding
A.1.1. NAS that only indicates PSMH
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0 |1|IHS|0| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |0| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=1 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL=0 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NAS that only indicates PSMH
In this example, as shown in Figure 5, the NAS may encode only the
presence of PSMH. The PSMH starts immediately after the BoS.
A.1.2. NAS that Indicates PSMH Start Offset
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=TBA1 | Post-Stack Offset = 2 |1|IHS|0| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |0| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=1 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL=0 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: NAS that Indicates PSMH Start Offset
The NAS may encode the start offset of the PSMH with a non-zero
value, for example, when it is after another header such as G-ACh or
Control Word header. In this example, as shown in Figure 6, the PSMH
starts at an offset of 8 octets after the BoS.
A.1.3. Post-Stack Network Actions with Two Opcodes
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NoOp| 0 |1|IHS|1| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=3 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=8|R|R| PS-NAL=0 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=9|R|R| PS-NAL=1 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Payload + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Post-Stack Network Actions with Two Opcodes
In this example, as shown in Figure 7, the PSMH encodes two different
Post-Stack Network Actions.
Details:
PSMH-Len=3: This is the length of PSMH contents after the Post-
Stack MPLS Base Header.
MNA-PS-OP=8: Post-Stack Network Action Opcode 8. A network action
allocation is outside of this document.
PS-NAL=0: Post-Stack Network Action does not contain any
additional data.
MNA-PS-OP=9: Post-Stack Network Action Opcode 9. A network action
allocation is outside of this document.
PS-NAL=1: Post-Stack Network Action contains one additional
4-octet AD.
A.1.4. Post-Stack Network Actions with Two Different Scopes
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NoOp| 0 |1|HbH|0| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=TBA1 | Post-Stack Offset = 2 |1|I2E|1| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=1 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=8|R|R| PS-NAL=0 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=2 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=9|R|R| PS-NAL=1 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Payload + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Post-Stack Network Actions with Two Different Scopes
In this example, as shown in Figure 8, the PSMH encodes two Post-
Stack Network Actions with different scopes. The first scope is HbH,
and the second scope is I2E.
Details:
The offset of the HbH-scoped Post-Stack Network Action is 0.
PSMH-Len=1: This is the length of PSMH contents after the first
Post-Stack MPLS Base Header.
MNA-PS-OP=8: Post-Stack Network Action Opcode 8. A network action
allocation is outside of this document.
PS-NAL=0: Post-Stack Network Action does not contain any
additional data.
Opcode TBA1 carries the offset of the I2E-scoped Post-Stack
Network Action. The data is 2, i.e., the PSMH starts 8 octets
after the BoS.
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PSMH-Len=2: This is the length of PSMH contents after the second
Post-Stack MPLS Base Header.
MNA-PS-OP=9: Post-Stack Network Action Opcode 9. A network action
allocation is outside of this document.
PS-NAL=1: Post-Stack Network Action contains one additional
4-octet AD.
A.2. Examples of In-Stack and Post-Stack Network Actions
A.2.1. NAS with In-Stack and Post-Stack Network Actions
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 (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |1|IHS|0| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |0| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=1 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=8|R|R| PS-NAL=0 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: NAS with In-Stack and Post-Stack Network Actions
In this example, as shown in Figure 9, the NAS may encode In-Stack
Network Actions and indicate the presence of a PSMH. The IHS field
indicates the scope of both the In-Stack and Post-Stack Network
Actions.
Details:
PSMH-Len=1: This is the length of PSMH contents after the first
Post-Stack MPLS Base Header.
MNA-PS-OP=8: Post-Stack Network Action Opcode 8. A network action
allocation is outside of this document.
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PS-NAL=0: Post-Stack Network Action does not contain any
additional data.
A.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 (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |0|HbH|0| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label (value 4) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NoOp| 0 |1|I2E|1| NASL=0|U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 |Reserve| PSMH-Len=1 | Type = MNA Post-Stack Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=8|R|R| PS-NAL=0 | Post-Stack Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: NASes with Different In-Stack and Post-Stack Scopes
In this example, as shown in Figure 10, the label stack may carry In-
Stack Network Actions with HbH scope and Post-Stack Network Actions
with I2E scope. In this case, there will be two NASes in the label
stack. The first NAS will encode the In-Stack Network Action with
the HbH scope and the second NAS will encode the presence of an I2E-
scoped Post-Stack Network Action.
Details:
PSMH-Len=1: This is the length of PSMH contents after the first
Post-Stack MPLS Base Header.
MNA-PS-OP=8: Post-Stack Network Action Opcode 8. A network action
allocation is outside of this document.
PS-NAL=0: Post-Stack Network Action does not contain any
additional data.
A.2.3. NAS with a BIER Header
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
| MNA Label (value 4) | TC |0| TTL | N
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A
| Opcode=TBA1 |Post-Stack Offset = 2+N |1|I2E|0| NASL=0|U|NAL=0| S
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
| BIFT-id (20 bits) | TC |1| TTL | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ B
| 0101b | Ver=0 | BSL | Entropy | I
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ E
|OAM|Rsv| DSCP | Proto | BFIR-id | R
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ H
| | D
~ BitString (N*4 octets) ~ R
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
| 0x0 |Reserve| PSMH-Len=1 | Type = MNA Post-Stack Header | P
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ S
| MNA-PS-OP |R|R| PS-NAL=0 | Post-Stack Data | MH
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: NAS with a BIER Header
In this example, as shown in Figure 11, a multicast packet with a
BIER header, defined in Section 2 of [RFC8296], carries an MPLS
encapsulation that is processed by non-BFR nodes. A NAS is carried
before the BIER header in the MPLS label stack and the associated
PSMH is carried below the BIER header.
The PSMH start offset is the length of the BIER header that follows
the BoS, in 4-octet units: two 4-octet words plus the BitString (N
words), i.e., (2+N)*4 octets in Figure 11. The first four octets of
the BIER header are the BoS LSE itself and are not counted for the
offset.
Acknowledgments
The authors would like to thank the authors and contributors of RFC
9994, as this document borrows some text from an earlier version of
that document. The authors would like to thank Greg Mirsky, Loa
Andersson, Haoyu Song, Adrian Farrel, Yao Liu, and Joel Halpern for
reviewing this document and providing many useful comments. The
authors also thank Chongfeng Xie for the OpsDir review and Tony
Rajamanickam, et al. Expires 31 January 2027 [Page 26]
Internet-Draft Post-Stack MNA Specification July 2026
Przygienda for the RtgDir review, which helped improve this document.
Thank you Ketan Talaulikar for the IESG review and providing many
useful comments to improve this document.
Contributors
The following people have substantially contributed to this document:
John Drake
Juniper Networks
United States
Email: je_drake@yahoo.com
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
Jie Dong
Huawei Technologies
Beijing
China
Email: jie.dong@huawei.com
Jisu Bhattacharya
Cisco Systems, Inc.
U.S.A.
Email: jisu@cisco.com
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