Post-Stack MPLS Network Action (MNA) Solution
draft-ietf-mpls-mna-ps-hdr-01
The information below is for an old version of the document.
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| Authors | Jaganbabu Rajamanickam , Rakesh Gandhi , Royi Zigler , Tony Li , Jie Dong | ||
| Last updated | 2025-08-05 (Latest revision 2025-05-30) | ||
| Replaces | draft-jags-mpls-ps-mna-hdr | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-mpls-mna-ps-hdr-01
MPLS Working Group J. Rajamanickam, Ed.
Internet-Draft R. Gandhi, Ed.
Intended status: Standards Track Cisco Systems, Inc.
Expires: 1 December 2025 R. Zigler
Broadcom
T. Li
Juniper Networks
J. Dong
Huawei Technologies
30 May 2025
Post-Stack MPLS Network Action (MNA) Solution
draft-ietf-mpls-mna-ps-hdr-01
Abstract
This document defines the Post-Stack MPLS Network Action (MNA)
solution for carrying Network Actions and Ancillary Data after the
MPLS label stack, based on the In-Stack MNA solution defined in "MPLS
Network Action (MNA) Sub-Stack Solution." MPLS Network Actions can
be used to influence packet forwarding decisions, carry additional
Operations, Administration, and Maintenance (OAM) information in the
MPLS packet, or perform user-defined operations. This solution
document addresses the Post-Stack network action and Post-Stack data
specific requirements found in "Requirements for MPLS Network
Actions." This document follows the architectural framework for the
MPLS Network Actions (MNA) technologies specified in "MPLS Network
Actions (MNA) Framework."
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 December 2025.
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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 Header Presence in In-Stack MNA Sub-Stack . . 5
3.2. Post-Stack Header Encoding . . . . . . . . . . . . . . . 6
3.2.1. Post-Stack Header Type . . . . . . . . . . . . . . . 6
3.2.2. Post-Stack Network Action Encoding . . . . . . . . . 7
4. In-Stack Network Action Special Opcodes . . . . . . . . . . . 7
4.1. In-Stack Network Action Opcode for PSH Start Offset . . . 7
4.2. In-Stack Network Action Opcode for PSH 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. Node Responsibilities . . . . . . . . . . . . . . . . . . . . 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. First Nibble for Post-Stack Header . . . . . . . . . . . 10
8.2. Post-Stack Header Types Registry . . . . . . . . . . . . 10
8.3. In-Stack Network Action Opcodes . . . . . . . . . . . . . 11
8.4. Post-Stack Network Action Opcodes . . . . . . . . . . . . 12
9. Appendix A: Examples . . . . . . . . . . . . . . . . . . . . 12
9.1. Examples of Post-Stack Header Encoding . . . . . . . . . 12
9.1.1. NAS that only Indicates Post-Stack Header . . . . . . 12
9.1.2. NAS that Indicates Post-Stack Header Start Offset . . 13
9.1.3. Post-Stack Network Actions with Two Opcodes . . . . . 14
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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
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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 Operations, Administration, and Maintenance (OAM)
logging, for example. AD can be used to carry additional
information, such as for In Situ OAM (IOAM) as described in
[I-D.ietf-mpls-mna-usecases]. User-defined network actions allow
local actions to be defined. In some cases, more AD may be required
to be carried in the MPLS header, so these kinds of network actions
and their AD are encoded after the Bottom of Stack (BOS). This
network action with AD is called Post-Stack Data.
This document defines the Post-Stack MPLS Network Action (MNA)
solution for carrying Network Actions and Ancillary Data after the
MPLS label stack. It is based on the In-Stack MNA solution defined
in [I-D.ietf-mpls-mna-hdr]. This solution document addresses the
Post-Stack network action and Post-Stack data specific requirements
found in [I-D.ietf-mpls-mna-requirements]. This document follows the
architectural framework for the MPLS Network Actions (MNA)
technologies specified in [I-D.ietf-mpls-mna-fwk].
2. Conventions Used in This Document
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
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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 Header| This document |
| |Presence Bit | |
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+------------+-----------------+----------------------------------+
|PSD |Post-Stack Data | [I-D.ietf-mpls-mna-requirements] |
| | | and [I-D.ietf-mpls-mna-fwk] |
+------------+-----------------+----------------------------------+
|PSH |Post-Stack Header| This document |
+------------+-----------------+----------------------------------+
|TC |Traffic Class | [RFC5462] |
+------------+-----------------+----------------------------------+
|TTL |Time To Live | [RFC3032] |
+------------+-----------------+----------------------------------+
Table 1: Abbreviations
3. Overview
The Post-Stack MNA solution contains two main parts:
* Post-Stack Header Presence in In-Stack MNA Sub-Stack
* Post-Stack Header Encoding that includes Post-Stack Header Type
and Post-Stack Network Actions
3.1. Post-Stack Header Presence in In-Stack MNA Sub-Stack
A reserved bit (21st bit from the left in LSE Format B
[I-D.ietf-mpls-mna-hdr]) in the In-Stack Network Action Sub-Stack
(NASS) described in [I-D.ietf-mpls-mna-hdr] is defined as P bit in
this document to indicate the presence of the Post-Stack Header in
the packet after the BOS.
The Post-Stack Header is encoded after the MPLS Label Stack (BOS),
either immediately after the BOS (i.e., start offset of 0) or after
any other Post-Stack headers that follow the BOS (i.e., start offset
of non-zero).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |P|IHS|S|U| NASL | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Post-Stack Header Presence in In-Stack MNA Sub-Stack
The following flags as defined in [I-D.ietf-mpls-mna-hdr] are also
applicable to Post-Stack Header:
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* IHS (2 Bit): Indicates the combined scope of the In-Stack and the
Post-Stack Network Actions. NASS for each scope with P bit set
will have its corresponding Post-Stack Header.
* U (1 Bit): Indicates the combined Unknown Action Handling of the
In-Stack and the Post-Stack Network Actions.
3.2. Post-Stack Header Encoding
The Post-Stack Header is encoded after the Bottom of the MPLS Label
Stack (BOS). The Post-Stack Header carry one ore more Post-Stack
Network Actions and their Ancillary Data.
The PSH consist of two main parts:
* Post-Stack Header (PSH) Type
* Post-Stack Network Action Encoding
3.2.1. Post-Stack Header Type
The Post-Stack Header type is the top-header for all the Post-Stack
Network Actions that are encoded in the PSH for each scope.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Post-Stack Header Type
* TBA1 (4 bits): This first nibble [I-D.ietf-mpls-1stnibble]
identifies the start of the PSH. A new value (value TBA1) is to
be assigned by IANA for PSH. Editor's note: Generic Associated
Channel (0001b) or CW (0000b) can be used.
* Version (4 bits): This is PSH version. The initial version is set
to 0.
* PS-HDR-LEN (8 bits): PSH Total Length in 4-octet units that
includes Post-Stack Network Actions. This excludes the PSH type
header.
* TYPE (16 bits): Type is set to MNA-POST-STACK-HDR as value 1 for
MNA, to be allocated by IANA.
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3.2.2. Post-Stack Network Action Encoding
The format shown in Figure 3, encodes a single Post-Stack Network
Action. By repeating this format, multiple Post-Stack Network Action
and its corresponding Ancillary data can be encoded.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Post-Stack Network Action Encoding
* MNA-PS-OP (7 bits): Post-Stack Network Action Opcode. Opcode "0"
is reserved and other opcodes will be assigned by IANA
accordingly.
* R (2 bits): Reserved bits.
* PS-NAL (7 bits): Post-Stack Network Action Length in 4-octet
units. This excludes the first 4-octets starting MNA-PS-OP.
* POST-STACK DATA (16 bits): Post-Stack Data associated with the
Post-Stack Network Action.
4. In-Stack Network Action Special Opcodes
4.1. In-Stack Network Action Opcode for PSH Start Offset
Opcode: TBA2
Purpose: This opcode carries the start offset of the PSH from BOS.
LSE Format: B (defined in [I-D.ietf-mpls-mna-hdr])
Data: The data value of the LSE contains the offset from the MPLS BOS
in units of 4 octets. This allows the Generic Control Word (0000b)
[RFC4385] and G-ACh (0001b) [RFC5586] fields to be placed immediately
after the BOS. In the absence of this opcode, the PSH is encoded
immediately after the MPLS BOS. A data value of 1 indicates that the
PSH starts 4 octets after the BOS.
Scope: This opcode can be used with any scope.
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4.2. In-Stack Network Action Opcode for PSH Depth Offset
Opcode: TBA3
Purpose: This opcode carries the depth of the Post-Stack Header
offset from BOS.
LSE Format: B or C (defined in [I-D.ietf-mpls-mna-hdr])
Data: The data value of the LSE contains the offset from the MPLS BOS
in units of 4 octets. A data value of 5 indicates that the Post-
Stack Header ends 20 octets after the BOS.
Scope: This opcode can be used with any scope.
5. Procedure
5.1. Processing Rules for P Bit
The P bit MUST be set to 1 in In-Stack Network Action Sub-Stack when
corresponding Post-Stack Header is added in the packet.
By default, the PSH starts immediately after the BOS. The offset for
the PSH that does not start immediately after the BOS is indicated
using the PSH Start Offset Opcode TBA2.
The P bit MUST be set to 1 when the network action with opcode TBA2
is added to the In-Stack Network Action Sub-Stack. The node that
recognizes the network action with Opcode TBA2 MUST process the
packet according to the U flag if the P bit is not set.
The P bit MUST be set to 1 when the network action with opcode TBA3
is added to the In-Stack Network Action Sub-Stack. The node that
recognizes the network action with Opcode TBA3 MUST process the
packet according to the U flag if the P bit is not set.
The node that supports the P bit, processes the Post-Stack Network
Actions in the Post-Stack Header as defined in this document.
Conversely, the node that does not support the P bit, will skip
processing the Post-Stack Header altogether.
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5.2. Network Action Processing Order
The Post-Stack Network Actions are processed in the same order they
are encoded after the BOS. By default, they are processed after the
In-Stack Network Actions in the Network Action Sub-Stack. However,
Post-Stack Network Action Opcodes for applications (such as IOAM as
described in [I-D.ietf-mpls-mna-usecases]) can be added in the In-
Stack Network Action Sub-Stack to process Post-Stack Network Actions
in a certain order with respect to the Opcodes in the In-Stack
Network Action Sub-Stack.
5.3. Node Capability Signaling
The ingress node that is adding a Post-Stack Header MUST ensure that
the egress node is capable of Post-Stack MNA and can remove the PSH
from the packet.
* Each participating node MUST signal the network actions that it
supports.
* Each participating node MUST signal its "Readable Label Depth
including Post-Stack Header" that can be encoded.
The above capability signaling will be added in appropriate
protocols. Signaling details are outside the scope of this document.
6. Node Responsibilities
This section defines the specific responsibilities for nodes along an
MPLS path for processing a Post-Stack Header.
6.1. Encapsulating Node Responsibilities
The encapsulating node MAY add Post-Stack Header to the packet in
accordance with its policies, the placement restrictions, and the
limitations.
The encapsulating node MUST NOT add a Post-Stack Header to the packet
if the decapsulation node does not support Post-Stack Header.
If the encapsulating node is also a transit node, then it MUST also
respect transit node responsibilities.
6.2. Transit Node Responsibilities
A transit node MAY modify the Ancillary Data in the Post-Stack
Header.
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A transit node MUST respect the Unknown Action Handling flag encoded
in the corresponding NAS when processing the PSH.
A node that removes the last copy of a NAS that has the P bit set
MUST remove all Post-Stack Headers.
6.3. Penultimate Node Responsibilities
In addition to the transit node responsibilities above, the
penultimate node MUST NOT remove the last copy of an HBH or I2E NAS
and associated PSH when it is exposed after removing the forwarding
(transport) label. This allows the egress node to process the NAS
and associated PSH.
6.4. Decapsulating Node Responsibilities
The decapsulating node MUST remove any Post-Stack Header it receives.
7. Security Considerations
The security considerations in [RFC3032], [I-D.ietf-mpls-mna-fwk],
and [I-D.ietf-mpls-mna-hdr] also apply to this document.
8. IANA Considerations
8.1. First Nibble for Post-Stack Header
This document requests that IANA allocate a value (TBA1) for the
First Nibble (value TBA1) for Post-Stack Header from the registry
"Post-Stack First Nibble" created by [I-D.ietf-mpls-1stnibble] to
indicate the start of the PSH after BOS.
+=======+====================================+===============+
| Value | Description | Reference |
+=======+====================================+===============+
| TBA1 | First Nibble for Post-Stack Header | This document |
+-------+------------------------------------+---------------+
Table 2: First Nibble for Post-Stack Header
8.2. Post-Stack Header Types Registry
This document requests that IANA create a new registry with the name
"Post-Stack Header Types" as follows. The registration procedure for
this registry is "IETF Review", "Experimental Use" and "Private Use".
The fields are "Type" (integer), "Description" (string), and
"Reference" (string).
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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 3: Post-Stack Header Types Registry
The initial assignment for this registry is:
+======+================================+===============+
| Type | Description | Reference |
+======+================================+===============+
| 1 | Post-Stack Header Type For MNA | This document |
+------+--------------------------------+---------------+
Table 4: Post-Stack Header Type For MNA
8.3. In-Stack Network Action Opcodes
The opcodes for In-Stack Network Action to be allocated by IANA from
the "In-Stack Network Action Opcode registry" to be created by in
[[I-D.ietf-mpls-mna-hdr]] as defined in this document as follows.
+========+=======================================+===============+
| Opcode | Description | Reference |
+========+=======================================+===============+
| TBA2 | Offset for Start of Post-Stack Header | This document |
+--------+---------------------------------------+---------------+
| TBA3 | Offset for Depth of Post-Stack Header | This document |
+--------+---------------------------------------+---------------+
Table 5: In-Stack Network Action Opcodes
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8.4. Post-Stack Network Action Opcodes
This document requests that IANA create a new registry with the name
"Post-Stack Network Action Opcodes". The registration procedure for
this registry is "IETF Review", "Experimental Use" and "Private Use".
The fields are "Opcode" (integer), "Description" (string), and
"Reference" (string). Opcode is an integer 0-127.
The assignments for this registry are:
+=========+==============================+===============+
| Opcode | Description | Reference |
+=========+==============================+===============+
| 0 | Reserved, not to be assigned | This document |
+---------+------------------------------+---------------+
| 1-110 | IETF Review | This document |
+---------+------------------------------+---------------+
| 111-114 | Experimental Use | This document |
+---------+------------------------------+---------------+
| 115-126 | Private Use | This document |
+---------+------------------------------+---------------+
| 127 | Reserved, not to be assigned | This document |
+---------+------------------------------+---------------+
Table 6: Post-Stack Network Action Opcodes Registry
9. Appendix A: Examples
9.1. Examples of Post-Stack Header Encoding
9.1.1. NAS that only Indicates Post-Stack 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 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|IHS|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ [0| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=1 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: NAS that only indicates Post-Stack Header
In some cases, the NAS may encode only the presence of Post-Stack
Header. The Post-Stack Header starts immediately after the BOS.
9.1.2. NAS that Indicates Post-Stack Header Start Offset
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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 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=TBA2 | Post-Stack Offset = 2 |1|IHS|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ [0| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=1 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NAS Indicates Post-Stack Header Start Offset
The NAS may encode the start offset for the Post-Stack Header with a
non-zero value, for example, when it is after other header such as
GACH or CW header. In this example, the PSH starts at offset of 8
bytes after the BoS.
9.1.3. Post-Stack Network Actions with Two Opcodes
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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 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|IHS|1|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=3 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=2|R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=3|R|R| PS-NAL=1 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Payload + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Post-Stack NA with Two Opcodes
This is an example, Post-Stack Header encodes two different Post-
Stack Network Actions.
Details:
PS-HDR-LEN=3: This is the Total Length of Post-Stack Header.
MNA-PS-OP=2: Post-Stack NA Opcode 2.
PS-NAL=0: Post-Stack Network Action does not contain any
additional data.
MNA-PS-OP=3: Post-Stack NA Opcode 3.
PS-NAL=1: Post-Stack Network Action contains 1 additional 4-octet
Ancillary data.
9.1.4. Post-Stack Network Action with two Different Scopes
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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 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|HBH|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=TBA2 | Post-Stack Offset = 2 |1|I2E|1|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=1 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=2|R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=2 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP=3|R|R| PS-NAL=1 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Payload + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Post-Stack NA with two Different Scopes
This is an example of Post-Stack Header encoding, that encode two
different different scoped Post-Stack Network Actions. The first
scope is Hop-By-Hop and the second scope is Ingress-To-Egress scoped
Post-Stack Network Action.
Details:
The offset of the Hop-By-Hop scoped Post-Stack Network Action 0.
Opcode TBA2 carries the offset of the Ingress-To-Egress scoped
Post-Stack Network Action. The data is 2, i.e., the Post-Stack
Header starts 8 bytes after the MPLS Bottom of Stack.
9.2. In-Stack and Post-Stack Network Actions
9.2.1. NAS with In-Stack and Post-Stack NAs
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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 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |1|IHS|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ [0| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=1 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: NAS with In-Stack and Post-Stack NAs
In some cases, the NAS may encode In-Stack NAs and indicate the
presence of Post-Stack Header. The IHS field indicates the scope of
both the In-Stack and Post-Stack NAs.
9.2.2. NASes with Different In-Stack and Post-Stack Scopes
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |0|HBH|0|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=2=NOOP| 0 |1|I2E|1|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA1 |Version| PS-HDR-LEN=1 | TYPE = MNA-POST-STACK-HDR = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-PS-OP |R|R| PS-NAL=0 | POST-STACK DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 9: NASes with Different In-Stack and Post-Stack Scopes
In some cases the label stack may need to carry In-Stack NAs with
Hop-By-Hop scope and Post-Stack NAs with I2E scope. In this case,
there will be two NASes in the label stack. In this case, the first
NAS will encode the In-Stack NA with the Hop-By-Hop scope and the
second NAS will encode the presence of I2E scoped Post-Stack NAs.
10. References
10.1. Normative References
[I-D.ietf-mpls-mna-fwk]
Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions (MNA) Framework", Work in Progress,
Internet-Draft, draft-ietf-mpls-mna-fwk-15, 27 December
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
mpls-mna-fwk-15>.
[I-D.ietf-mpls-mna-requirements]
Bocci, M., Bryant, S., and J. Drake, "Requirements for
Solutions that Support MPLS Network Actions (MNA)", Work
in Progress, Internet-Draft, draft-ietf-mpls-mna-
requirements-16, 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-
12, 3 March 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-mpls-mna-hdr-12>.
[I-D.ietf-mpls-1stnibble]
Kompella, K., Bryant, S., Bocci, M., Mirsky, G.,
Andersson, L., and J. Dong, "IANA Registry and Processing
Recommendations for the First Nibble Following a Label
Stack", Work in Progress, Internet-Draft, draft-ietf-mpls-
1stnibble-13, 5 December 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
1stnibble-13>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, 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>.
[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>.
[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>.
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,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-usecases-15>.
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Acknowledgments
The authors would like to thank the authors and contributors of the
draft-ietf-mpls-mna-hdr as this document borrows some text from the
earlier version of that document. The authors would like to thank
Greg Mirsky, Loa Andersson, Haoyu Song, and Joel Halpern for
reviewing this document and providing many useful comments.
Contributors
The following people have substantially contributed to this document:
Jisu Bhattacharya
Cisco Systems, Inc.
Email: jisu@cisco.com
John Drake
Juniper Networks
United States
Email: jdrake@juniper.net
Authors' Addresses
Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
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
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Jie Dong
Huawei Technologies
Beijing
China
Email: jie.dong@huawei.com
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