MNA for Metadata in SR-MPLS Service Programming
draft-liu-mpls-mna-sr-service-metadata-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Yao Liu | ||
| Last updated | 2025-06-23 | ||
| Replaces | draft-liu-spring-sr-sfc-metadata | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-liu-mpls-mna-sr-service-metadata-01
MPLS Y. Liu
Internet-Draft ZTE
Intended status: Standards Track 23 June 2025
Expires: 25 December 2025
MNA for Metadata in SR-MPLS Service Programming
draft-liu-mpls-mna-sr-service-metadata-01
Abstract
This document defines MPLS Network Action(MNA) encoding to carry
metadata in SR service programming with SR-MPLS data plane.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 25 December 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. MPLS Network Action ISD encoding for Metadata in SR-MPLS
Service Programming . . . . . . . . . . . . . . . . . . . 3
3.1. Fixed-Length Service Metadata . . . . . . . . . . . . . . 3
3.2. Variable-Length Service Metadata . . . . . . . . . . . . 4
4. Post-Stack MNA Encoding for Metadata in SR-MPLS Service
Programming . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Post-Stack Fixed-Length Metadata in SR-MPLS Service
Programming . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Post-Stack Variable-Length Metadata in SR-MPLS Service
Programming . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. In-Stack MPLS Network Action Opcodes . . . . . . . . . . 8
5.2. Post-Stack MPLS Network Action Opcodes . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[I-D.ietf-spring-sr-service-programming] defines data plane
functionality required to implement service segments and achieve
service programming in SR-enabled MPLS and IPv6 networks.
Metadata[RFC7665] provides contextual information about the data
packets which traverse a programmed service path.
However, there's yet no standard method to carry service metadata
with the SR-MPLS data plane, which make the solution for service
programming in SR-MPLS incomplete
MPLS Network Action (MNA) [I-D.ietf-mpls-mna-fwk] is used to indicate
action for Label Switched Paths (LSPs) and/or MPLS packets, and to
transfer data needed for the action. [I-D.ietf-mpls-mna-hdr] defines
the MNA sub-stack solution for carrying Network Action Indicators and
Ancillary Data in the label stack.
This document defines MPLS Network Action(MNA) encoding to carry
metadata in SR service programming with SR-MPLS data plane.
2. Terminology
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2.1. Acronyms
HBH: Hop-By-Hop
I2E: Ingress-To-Egress
IHS: Ingress-To-Egress (I2E), Hop-By-Hop (HBH) or Select Scope
ISD: In-Stack Data
PSD: Post-Stack Data
PSH: Post-Stack Header
LSE: Label Stack Entry
MPLS: Multiprotocol Label Switching
MNA: MPLS Network Action
2.2. 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.
3. MPLS Network Action ISD encoding for Metadata in SR-MPLS Service
Programming
The metadata in SR-MPLS Service Programming is placed as part of the
ISD block in an MPLS label stack according to the MNA encoding
principles defined in [I-D.ietf-mpls-mna-hdr]. Two types of metadata
for SR-MPLS service programming are defined: fixed-length service
metadata and variable-length service metadata.
3.1. Fixed-Length Service Metadata
The format of fixed-length service metadata is shown as follows,
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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 |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode = TBA1 | Service Metadata |R|IHS|S|U| NASL | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Service Metadata |S| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Service Metadata |S| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Service Metadata |S| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* The MNA Label is defined in [I-D.ietf-mpls-mna-hdr].
* S: the Bottom of Stack field [RFC3032].
* Opcode: TBA1, indicating the fixed-length service metadata.
* R,IHS and U fields are set as specified in
[I-D.ietf-mpls-mna-hdr].
* NASL: The Network Action Sub-Stack Length (NASL) as specified in
[I-D.ietf-mpls-mna-hdr]. The value is 3.
* NAL: Network Action Length as specified in
[I-D.ietf-mpls-mna-hdr]. The number of extra LSEs used for
Service metadata encoding. The value is 3.
* Service Metadata: 102-bit field to carry metadata. No assumption
is made by this document on the structure or the content of the
carried metadata.
3.2. Variable-Length Service Metadata
It should be noticed that although it is called "variable-length",
the length of this service metadata MUST NOT be changed on the fly.
The format of variable-length service metadata is shown as follows,
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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 |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode = TBA2 | MD Class | Type |R|IHS|S|U| NASL | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~1| Service Metadata |S| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* The MNA Label is defined in [I-D.ietf-mpls-mna-hdr].
* S: the Bottom of Stack field [RFC3032].
* Opcode: TBA2, indicating the variable-length service metadata.
* R,IHS and U fields are set as specified in
[I-D.ietf-mpls-mna-hdr].
* NASL: The Network Action Sub-Stack Length (NASL) as specified in
[I-D.ietf-mpls-mna-hdr].
* NAL: Network Action Length as specified in
[I-D.ietf-mpls-mna-hdr]. The number of extra LSEs used for
Service metadata encoding.
* Metadata Class (MD Class): Defines the scope of the Type field to
provide a hierarchical namespace.
* Type: Indicates the explicit type of metadata being carried. The
definition of the Type is the responsibility of the MD Class
owner.
* Service Metadata: The field length depends on the value of NAL.
4. Post-Stack MNA Encoding for Metadata in SR-MPLS Service Programming
The presence of Post-Stack Header is indicated in an In-Stack Network
Action Sub-stack as defined in [I-D.ietf-mpls-mna-ps-hdr] and is
shown as below.
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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 |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |P|IHS|S|U| NASL | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Post-Stack Service Metadata ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
~ Optional Payload + Padding ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* The MNA Label is defined in [I-D.ietf-mpls-mna-hdr].
* P flag is set as specified in [I-D.ietf-mpls-mna-ps-hdr]
* The IHS scope field defined in [I-D.ietf-mpls-mna-hdr] is used to
indicate that I2E or HBH or Select processing is required for the
Network Action and Ancillary Data.
* S: the Bottom of Stack field [RFC3032].
* U: set as specified in [I-D.ietf-mpls-mna-hdr].
* NASL: The Network Action Sub-Stack Length (NASL) as specified in
[I-D.ietf-mpls-mna-hdr].
* NAL: Network Action Length as specified in
[I-D.ietf-mpls-mna-hdr]. The value is 0.
* Opcode: TBA3, In-Stack Network Action for the service metadata in
PSH.
* Data (10 bits, next to the Opcode field) in the LSE contains the
offset for PSH for this In-Stack Network Action in 4-octets units
after BOS LSE to the start of the corresponding Post-Stack Network
Action Opcode. Due to the Post-Stack Header type top-header,
minimum value for the offset is 1 (i.e, 4-octets).
* Post-Stack Service Metadata: the service metadata carried in PSH,
see section 4.1 and section 4.2.
4.1. Post-Stack Fixed-Length Metadata in SR-MPLS Service Programming
The encoding of the post-stack variable-length service metadata is
shown as follows,
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Post-Stack MNA Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
|MNA-PS-OP |R|R| PS-NAL | Service Metadata |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Service Metadata |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
Where:
* Post-Stack MNA Header: the top-level header for all the Post-Stack
Network Actions that are encoded as defined in
[I-D.ietf-mpls-mna-ps-hdr].
* MNA-PS-OP: TBA4 for post-stack fixed -length service metadata.
* R (2 bits): Reserved bits.
* PS-NAL (7 bits): Post-Stack Network Action Length in 4-octet units
as in [I-D.ietf-mpls-mna-ps-hdr]. This excludes the first
4-octets starting PS-MNA-OP. The value is 3.
* Service Metadata: 14-byte field carrying the service metadata. No
assumption is made by this document on the structure or the
content of the carried metadata.
4.2. Post-Stack Variable-Length Metadata in SR-MPLS Service Programming
The encoding of the post-stack variable-length service metadata is
shown as follows,
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Post-Stack MNA Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
|MNA-PS-OP |R|R| PS-NAL | MD Class | Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Service Metadata ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
Where:
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* Post-Stack MNA Header: the top-level header for all the Post-Stack
Network Actions that are encoded as defined in
[I-D.ietf-mpls-mna-ps-hdr].
* MNA-PS-OP: TBA5 for post-stack variable-length service metadata.
* R (2 bits): Reserved bits.
* PS-NAL (7 bits): Post-Stack Network Action Length in 4-octet units
as in [I-D.ietf-mpls-mna-ps-hdr]. This excludes the first
4-octets starting PS-MNA-OP.
* Metadata Class (MD Class): Defines the scope of the Type field to
provide a hierarchical namespace.
* Type: Indicates the explicit type of metadata being carried. The
definition of the Type is the responsibility of the MD Class
owner.
* Service Metadata: Metadata for SR-MPLS Service Programming, the
length of field depends in the value of PS-NAL.
5. IANA Considerations
5.1. In-Stack MPLS Network Action Opcodes
IANA is requested to assign codepoints from its Network Action
Opcodes registry (creation requested in [I-D.ietf-mpls-mna-hdr]) as
specified in Table 1.
+------+--------------------------------+-------------+
|Opcode| Name | Reference |
| | | |
+------+--------------------------------+-------------+
| TBA1 | In-Stack Network Action for | |
| | Fixed-Length Service Metadata |This document|
| | in ISD | |
+------+--------------------------------+-------------+
| TBA2 | In-Stack Network Action for | |
| |Variable-Length Service Metadata|This document|
| | in ISD | |
+------+--------------------------------+-------------+
| TBA3 | In-Stack Network Action for |This document|
| | Service Metadata in PSH | |
+------+--------------------------------+-------------+
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5.2. Post-Stack MPLS Network Action Opcodes
IANA is requested to assign codepoints for the Post-Stack Network
Action for the post-stack service metadata from the Post-Stack
Network Action Opcodes registry (to be created by in
[I-D.ietf-mpls-mna-hdr]).
+------+--------------------------------+-------------+
|Opcode| Name | Reference |
| | | |
+------+--------------------------------+-------------+
| TBA4 | Post-Stack Network Action for |This document|
| | Fixed-Length Service Metadata | |
+------+--------------------------------+-------------+
| TBA5 | Post-Stack Network Action for |This document|
| |Variable-Length Service Metadata| |
+------+--------------------------------+-------------+
6. Security Considerations
Security considerations discussed in [I-D.ietf-mpls-mna-fwk],
[I-D.ietf-mpls-mna-hdr], [I-D.ietf-mpls-mna-ps-hdr] and
[I-D.ietf-spring-sr-service-programming] apply to this document.
7. References
7.1. 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-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>.
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[I-D.ietf-mpls-mna-ps-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Li, T., and J.
Dong, "Post-Stack MPLS Network Action (MNA) Solution",
Work in Progress, Internet-Draft, draft-ietf-mpls-mna-ps-
hdr-01, 30 May 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-ps-hdr-01>.
[I-D.ietf-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C.,
Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and
S. Salsano, "Service Programming with Segment Routing",
Work in Progress, Internet-Draft, draft-ietf-spring-sr-
service-programming-11, 23 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-service-programming-11>.
[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>.
[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>.
7.2. Informative References
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
Author's Address
Yao Liu
ZTE
Nanjing
China
Email: liu.yao71@zte.com.cn
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