Markdown Version | Session Recording

Session Date/Time: 09 Sep 2024 14:00

IDR

Summary

This interim IDR meeting focused on the status of BGP LS and Segment Routing (SR) working group drafts, addressing allocation issues for SR policy segment types, and reviewing several drafts for Working Group Last Call (WGLC) or adoption. Key discussions included the distinction between unicast and multicast SR policy SAFIs, the need for SPRING Working Group review for composite and dynamic SR policies, common pitfalls in draft writing, and a specific issue regarding SRv6 segment list optimization. Decisions were made to proceed with WGLC for certain drafts and to address the SR policy registry formalization.

Key Discussion Points

• Logistics and Agenda:
  • The meeting was the first of four planned IDR interims for the fall.
  • SPRING Working Group chairs were initially unavailable, but Alo joined later.
  • Agenda covered IDR working group draft status on BGP LS and SR, allocation of sub-TLVs for SR Policy, and specific draft presentations.
• Status of Segment Routing (SR) Drafts:
  • draft-ietf-idr-sr-policy-safi and draft-ietf-idr-sr-seg-types are at the IESG, experiencing significant delays (estimated ~9 months).
  • Unicast vs. Multicast: It was clarified that unicast SR Policy uses sr-policy-safi and a distinct tunnel type, while multicast uses srp2mp-safi and a separate tunnel type. This distinction is not always clear in current drafts.
  • SR Policy Types:
    • Explicit: Well-defined, covered by draft-ietf-idr-sr-policy-safi and draft-ietf-idr-sr-seg-types.
    • Composite: Individual drafts exist, but require more review and discussion, particularly from the SPRING WG. Alo (SPRING co-chair) confirmed they need more review.
    • Dynamic: No mature drafts identified.
  • Dependent Drafts: Several proposed standard drafts dependent on sr-policy-safi (e.g., te-policy-attribute, sr-mpls-elp, segment-list-id, metric, path-mtu, path-segment) require editorial and technical work, and ideally, two implementations, before progressing to WGLC.
  • Multicast SR Drafts: p2mp-policy is early work and has expired. A new L2-bundle SR draft was recently approved. Both need review by SPRING and TE WGs.
  • Independent SR Drafts: Several individual drafts require more SPRING WG work before IDR adoption calls (e.g., s-policy-cp-valid, composite-path, head-end-behavior, segment-list-optimization, detnet-hold, policy-template, scheduling).
• Common Errors in SR Drafts for IESG Shepherd Reports:
  • Drafts must clearly link to RFC 912 (SAFI + tunnel encapsulation augmentation).
  • They should augment IDR BGP mechanisms, not just SR policy concepts.
  • Error handling for malformed TLVs and out-of-range values should align with RFC 7606.
  • Security sections should augment RFC 912 and draft-ietf-idr-sr-policy-safi, adding specific security considerations for the new information.
• SR Segment Type Allocation Issues:
  • draft-ietf-idr-sr-policy-safi defines a segment type registry (Section 6.5, "SR Policy Segment List Sub-TLV Types"), but its delay at the IESG means this registry is not yet officially created by IANA.
  • Currently, temporary "first come, first serve" allocations are managed on the IDR wiki, which may contain errors.
  • The chair discussed having IANA manage a temporary registry or accelerating an RFC to formalize it.
  • A poll of the room was taken regarding potential re-allocation if an "allocate with gaps" approach was chosen. Participants expressed concern about changing existing temporary code points already in use for implementations (e.g., for P-Segment and Segment List ID).
• Status of BGP LS Drafts:
  • draft-ietf-idr-bgp-ls-sr-policy and draft-ietf-idr-bgp-ls-path are ready for WGLC after minor edits, with known implementations.
  • draft-ietf-idr-bgp-ls-sr-policy-nrp is progressing.
  • Other drafts like link-mtu, sr-policy-path-segment, sr-service-segments need revisions. bgp-only-fabric requires further work before WGLC.
  • Individual BGP LS drafts (e.g., algo-related-adjacency, transport-slice, composite, p2mp-policy-distribution, flexible-path, savnet) require further concept development in SPRING or alignment with existing work.
• Presentations and Draft Reviews:
  • draft-ietf-idr-bgp-ls-sr-vpn-mt (Chunfen Gao): An informational draft describing BGP LS mechanisms for SR-based Network Resource Partitions (NRPs) using Multi-Topology ID. It reuses MTI-ID as a control plane ID for NRPs. The document has been updated to align with RFC 9543 and related drafts. The authors believe it is stable and ready for WGLC.
  • draft-ietf-idr-bgp-ls-sr-policy-nrp (Ge Ruan): Defines BGP LS SR Policy extensions to indicate association with a specific NRP via a new NRP sub-TLV in the BGP Tunnel Encapsulation attributes. It aims to augment packets with both SR list and NRP identifier. It requires further alignment on terminology with TE and SPRING WGs before WGLC. Alo confirmed that a companion SPRING document is forthcoming.
  • draft-ietf-idr-bgp-ls-sr-perf-metric (Chang Wang): Proposes a mechanism for advertising SR Policy performance metrics (delay, packet loss rate) via BGP LS from the headend device. It extends RFC 8571 definitions for unidirectional and bidirectional performance metrics within the Segment List TLV. The draft is requesting working group adoption.
  • draft-ietf-idr-sr6-segment-list-optimization (Yu Song): Addresses efficiency issues when SRv6 segment lists contain both an N-SID and a VPN service-SID for the egress node, potentially requiring double lookup or affecting forwarding efficiency. The proposal is to introduce an E-flag in the C-structure field to identify the egress node SID, allowing the N-SID to be omitted from the segment list in data packets. Alo suggested presenting the underlying problem to the SPRING WG mailing list for confirmation before IDR adoption.

Decisions and Action Items

• Decision: For the temporary allocation of SR policy segment list subtypes, the IDR WG will continue with a "first come, first serve" approach, maintaining existing allocations.
• Action Item (Chair): Sue Hares will pursue the creation of an RFC to formalize the SR policy segment list subtypes registry with IANA.
• Action Item (Chunfen Gao): draft-ietf-idr-bgp-ls-sr-vpn-mt will be put to Working Group Last Call.
• Action Item (Ge Ruan): Conduct further alignment of draft-ietf-idr-bgp-ls-sr-policy-nrp terminology with the TE and SPRING Working Groups before proceeding to Working Group Last Call.
• Action Item (Chang Wang): draft-ietf-idr-bgp-ls-sr-perf-metric will be put to Working Group Last Call.
• Action Item (Yu Song): Initiate a discussion on the SPRING WG mailing list to confirm the problem described in draft-ietf-idr-sr6-segment-list-optimization and solicit feedback before IDR considers adoption.
• Action Item (All Draft Authors): Review drafts to ensure clear links to RFC 912, correct augmentation of IDR BGP mechanisms, proper error handling per RFC 7606, and augmented security sections as per draft-ietf-idr-sr-policy-safi.

Next Steps

• Upcoming IDR Interims:
  • Link Bandwidth / Next-Hop Capability: Hosted by Jeff Haas (October 23).
  • Flowspec V2: Short interim for final draft review before adoption calls.
  • Secure VPN and SN Overlap: Potential discussion if SPRING chairs are available.
  • Initial Draft Feedback (Pre-IETF 121): October 14, for authors planning to present new drafts at IETF 121.
• Continued Work on Drafts: Authors of SR and BGP LS drafts are encouraged to address outstanding technical and editorial issues, seek implementations, and ensure alignment with dependent drafts and other working groups (e.g., SPRING, TE).
• SPRING WG Engagement: Several drafts require input and review from the SPRING WG to confirm problem statements and proposed solutions.