| Internet-Draft | BGP extensions for SRv6/MPLS Transport I | February 2026 |
| Agrawal, et al. | Expires 10 August 2026 | [Page] |
- Workgroup:
- IDR WorkGroup
- Internet-Draft:
- draft-sa-idr-bgp-srv6-mpls-transport-iw-02
- Published:
- Intended Status:
- Standards Track
- Expires:
BGP extensions for SRv6/MPLS Transport Interworking
Abstract
This document defines the BGP extensions required to provide transport interworking between SRv6 and MPLS in SRv6 deployment.¶
Status of This Memo
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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/.¶
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This Internet-Draft will expire on 10 August 2026.¶
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.¶
1. Introduction
The deployment of SRv6 into existing transport network require SRv6 to interwork with MPLS. [I-D.ietf-spring-srv6-mpls-interworking] describes SRv6 and MPLS interworking architecture in multi domain network where each domain run SRv6 or MPLS data plane independently. To accomplish it, section 7.1.2 of [I-D.ietf-spring-srv6-mpls-interworking] details BGP inter-domain routing procedure in which domain border router set next hop to self when propagating transport routes (for example, locator or loopback prefix of a PE) across domains. Setting next hop to self results in allocation of label or SRv6 SID depending on dataplane type of the domain where route is propagated. Signaling of label is already specified in [RFC8277]. This document specifies method to signal SRv6 SID behaviors End.DTM and End.DTM46 specified in [I-D.ietf-spring-srv6-mpls-interworking] needed for SRv6 and MPLS interworking with BGP Labeled Unicast (BGP-LU) routes (SAFI value 4 routes as specified in [RFC8277]).¶
1.1. 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. Signal SRv6 SID for BGP transport route
The Prefix-SID attribute is an optional, transitive path attribute defined in [RFC8669] to announce information about BGP Segment identifiers as list of TLVs. [RFC8669] defined TLV type 1 to encode label index and TLV type 3 to encode Originator SRGB to be attached to prefixes of BGP-LU SAFI([RFC8277]). [RFC9252] extended Prefix-SID attribute to carry SRv6 Segment Identifier that is encoded in SRv6 Service TLV and attached to BGP service routes.¶
2.1. SRv6 Transport TLV
This document defines a new TLV called "SRv6 Transport TLV" of the BGP Prefix-SID Attribute to announce SRv6 SID with prefixes of BGP-LU SAFI. SRv6 SID is encoded in "SRv6 Transport TLV" exactly like SRv6 Service SID TLV [RFC9252]. This document uses the TLV to signal End.DTM and End.DTM46. The usage of this TLV for other SRv6 SID behaviors and SAFI's is out of scope of this document and may be extended in future documents. Extension in this document lead to signaling of label in MPLS label field and SRv6 SID in SRv6 Transport TLV for BGP-LU route. Below section describes usage of both the information based on behavior of the SRv6 SID.¶
2.2. SRv6 encapsulation for MPLS transport
SRv6 SID is used to encapsulate the MPLS packet whose top label is the label value in MPLS field of the NLRI of the BGP-LU route. Draft [I-D.ietf-spring-srv6-mpls-interworking] defines End.DTM and End.DTM46 pseudo-code for this purpose.¶
Domain border router that set next hop to self, allocates label bound to each prefix of BGP-LU route. Label is encoded in MPLS label field as specified in [RFC8277]. SRv6 SID is encoded in "SRv6 Transport TLV" without transposition i.e. transposition length MUST be set to 0 in SRv6 SID Structure Sub-Sub-TLV. Behavior field MUST be set with SRv6 Endpoint Behavior codepoint value of End.DTM or End.DTM46. This behavior signals "AND" semantics i.e. push label signaled in NLRI and perform H.Encaps.M [I-D.ietf-spring-srv6-mpls-interworking] with DA as SRv6 SID signaled in the TLV. Same SRv6 SID can be attached to multiple BGP-LU routes by domain border router that sets next hop to self.¶
Section 7.1.2.2 of [I-D.ietf-spring-srv6-mpls-interworking] describe control and dataplane state using SRv6 Transport TLV.¶
2.3. Propagation of transport routes with SRv6 SID
A BGP speaker that receive Prefix-SID attribute with SRv6 Transport TLV with transport route observe following rules when advertising the route to other peers:¶
-
If the nexthop is unchanged, the TLVs, including any unrecognized Types of Sub-TLV and Sub-Sub-TLV, SHOULD be propagated further. In addition, all Reserved fields in the TLV or Sub-TLV or Sub-Sub-TLV MUST be propagated unchanged.¶
-
If the nexthop is modified, the TLV and associated sub-TLVs/Sub-Sub-TLVs SHOULD be updated based on local policy. For example, if upstream is MPLS domain, then TLVs carrying SRv6 SID should be removed and local MPLS label bound to address in NLRI is propagated further.¶
3. Error Handling
SRv6 SID is encoded in "SRv6 Transport TLV" exactly like SRv6 Service SID TLV [RFC9252]. Hence, [RFC9252] error handling is applicable for "SRv6 Transport TLV" processing. Behavior codepoint other than End.DTM and End.DTM46 is out of the scope of this document. The path having such Prefix-SID attribute without any valid SRv6 SID behavior MUST be considered ineligible during the selection of the best path for the corresponding route.¶
4. IANA Considerations
4.1. BGP Prefix-SID TLV Types registry
This document introduce a new TLV Type of the BGP Prefix-SID attribute. IANA is requested to assign Type value in the registry "BGP Prefix-SID TLV Types" as follows¶
Value Type Reference
----------------------------------------------------------
TBD SRv6 Transport TLV <this document>¶
5. Security Considerations
This document defines new TLV of Prefix-SID attribute attached to transport route. Tranport route is signaled among the nodes under the single administrative domain and security considerations of the attribute described in [RFC8669] continues to apply.¶
6. Contributors
Zafar Ali Cisco Systems Email: zali@cisco.com¶
Daniel Voyer Cisco Systems Email: davoyer@cisco.com¶
Shraddha Hegde HPE Email:shraddha.hegde@hpe.com¶
7. Acknowledgements
The authors would like to acknowledge Stephane Litkowski and Ketan Talaulikar for review and comments.¶
8. References
8.1. Normative References
- [I-D.ietf-spring-srv6-mpls-interworking]
- Agrawal, S., Filsfils, C., Voyer, D., Dawra, G., Li, Z., and S. Hegde, "SRv6 and MPLS interworking", Work in Progress, Internet-Draft, draft-ietf-spring-srv6-mpls-interworking-01, , <https://datatracker.ietf.org/doc/html/draft-ietf-spring-srv6-mpls-interworking-01>.
- [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>.
- [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, , <https://www.rfc-editor.org/info/rfc3032>.
- [RFC4023]
- Worster, T., Rekhter, Y., and E. Rosen, Ed., "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)", RFC 4023, DOI 10.17487/RFC4023, , <https://www.rfc-editor.org/info/rfc4023>.
- [RFC4271]
- Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, , <https://www.rfc-editor.org/info/rfc4271>.
- [RFC4364]
- Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, , <https://www.rfc-editor.org/info/rfc4364>.
- [RFC4760]
- Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, , <https://www.rfc-editor.org/info/rfc4760>.
- [RFC7432]
- Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, , <https://www.rfc-editor.org/info/rfc7432>.
- [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>.
- [RFC8277]
- Rosen, E., "Using BGP to Bind MPLS Labels to Address Prefixes", RFC 8277, DOI 10.17487/RFC8277, , <https://www.rfc-editor.org/info/rfc8277>.
- [RFC8402]
- Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, , <https://www.rfc-editor.org/info/rfc8402>.
- [RFC8664]
- Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., and J. Hardwick, "Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing", RFC 8664, DOI 10.17487/RFC8664, , <https://www.rfc-editor.org/info/rfc8664>.
- [RFC8669]
- Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah, A., and H. Gredler, "Segment Routing Prefix Segment Identifier Extensions for BGP", RFC 8669, DOI 10.17487/RFC8669, , <https://www.rfc-editor.org/info/rfc8669>.
- [RFC8986]
- Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, , <https://www.rfc-editor.org/info/rfc8986>.
- [RFC9252]
- Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene, B., Zhuang, S., and J. Rabadan, "BGP Overlay Services Based on Segment Routing over IPv6 (SRv6)", RFC 9252, DOI 10.17487/RFC9252, , <https://www.rfc-editor.org/info/rfc9252>.
- [RFC9256]
- Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, , <https://www.rfc-editor.org/info/rfc9256>.
8.2. Informative References
- [I-D.ietf-mpls-seamless-mpls]
- Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz, M., and D. Steinberg, "Seamless MPLS Architecture", Work in Progress, Internet-Draft, draft-ietf-mpls-seamless-mpls-07, , <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-seamless-mpls-07>.