MNA for Metadata in SR-MPLS Service Programming

Internet-Draft	MNA for Metadata	June 2025
Liu	Expires 8 December 2025	[Page]

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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.¶

3. MNA 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,¶

 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 |   Servie Metadata     |R|IHS|S|U| NASL  | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|                       Servie Metadata     |S|               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|                       Servie Metadata     |S|               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|                       Servie 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 servie metadata encoding. The value is 3.¶
Opcode is MNA-IOAM-DEX opcode (value TBA2) to be assigned by IANA.¶
Servie Metadata: 102-bit field to carry metadata¶

3.2. Variable-Length Service Metadata

The format of 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               MNA Label               | TC  |S|    TTL        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode = TBA2 |   Servie Metadata     |R|IHS|S|U| NASL  | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~1|                      Servie 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 servie metadata encoding.¶
Servie Metadata: The field length depends on the value of NAL.¶

4. IANA Considerations

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    |This document|
     |      | Fixed-Length Servie Metadata   |             |
     +------+--------------------------------+-------------+
     | TBA2 | In-Stack Network Action for    |This document|
     |      | Variable-Length Servie Metadata|             |
     +------+--------------------------------+-------------+

6. References

6.1. 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>.
[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>.

6.2. 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>.

MNA for Metadata in SR-MPLS Service Programming

Abstract