| Internet-Draft | MNA for Metadata | June 2025 |
| Liu | Expires 25 December 2025 | [Page] |
- Workgroup:
- MPLS
- Internet-Draft:
- draft-liu-mpls-mna-sr-service-metadata-01
- Published:
- Intended Status:
- Standards Track
- Expires:
MNA for Metadata in SR-MPLS Service Programming
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
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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/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.¶
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
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,¶
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,¶
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.¶
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,¶
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:¶
- 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 | | +------+--------------------------------+-------------+¶
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, , <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, , <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-mna-hdr-12>.
- [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, , <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, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8300>.