Session Date/Time: 06 Nov 2025 14:30

PCE

Summary

The PCE Working Group met for a session at IETF 122 in Montreal. The chairs provided an update on the working group's robust progress, with three new RFCs published and two documents in the RFC Editor Queue. Several drafts are nearing Working Group Last Call, including those related to Circuit Style, State Sync, and Flex Grid, with discussions held regarding author attribution during retirement processes.

Key technical discussions included an update on SR Point-to-Multipoint Policy PCEP extensions, clarification on SRv6 MSD limitations within PCEP, and proposed B-SID extensions to handle unavailability and dynamic fallback. Significant debate occurred around multi-path support in PCEP, particularly concerning the alignment of backup path mechanisms with the SR policy architecture. New PCEP extensions were presented for deterministic latency metrics, BFD capabilities (including granularity for traffic types), and mechanisms to address PCE redundancy and allow LSP creation in a "down" state under certain conditions. The session concluded with an update on PCEP extensions for precision metrics, incorporating feedback from other working groups.

Key Discussion Points

Working Group Status:
- Three new RFCs published: PCM PSEP Yang Module, and PSEP extensions for Segment Routing policies and programs.
- Two documents are in the RFC Editor Queue: one on PSEP security and another related to SID.
- Four drafts are undergoing early IANA allocation, with a need to prioritize their progression.
- An ITU-T liaison provides updates coordinated with other working areas like TEAS and PLS.
WG Document Progress (AD Update):
- Post WG Last Call: Circuit Style (authors updated, early directorate reviews initiated), State Sync (shepherd review done, pending author updates), Flex Grid (author retirement handled, waiting for shepherd review).
- A discussion took place regarding handling author attribution for retired contributors (e.g., Francesco from Flex Grid draft), clarifying that authors can remain on the list and IETF processes support this, though authors ultimately decide.
- Several documents are identified as candidates for upcoming Working Group Last Call, with an emphasis on incorporating implementation and manageability sections.
- Auto-Bandwidth Update: Rakesh Kandhi (Cisco) presented updates to RFC 8733, extending auto-bandwidth procedures to SR (SR-MPLS and SRv6 LSPs).
- Segment Routing Documents: Chungli (Huawei) noted six to seven segment routing related documents, prioritizing those with IANA code point renewal deadlines, and coordinating with the Spring WG.
SR Point-to-Multipoint Policy PCEP Extensions:
- Humen (Nokia) reported on terminology alignment across P2MP policy (PIM), PCEP, and EVPN drafts, addressing AD and reviewer comments.
- The PCEP P2MP draft is ready for Working Group Last Call, with an early directorate review planned (Routing and Ops areas). Andrew (Cisco) confirmed that recent diffs reflect structural and grammatical changes, not technical alterations.
SRv6 MSD Limitations in PCEP:
- Ziti (ZTE) presented a draft addressing that existing RFC 9603 treats all SRv6 MSD types as strict limitations, but some (Max Pop MSD, Max ND MSD) are not always relevant for the head-end PCC.
- Proposed updating RFC 9603 to specifically consider "Max Edge Incap MSD" (which can be MSD+1 with Reduced SRH mode) and "Max Segment Left MSD" as limitations.
- Zaffer (individual) suggested consolidating this work with the agency SID draft due to overlaps and seeking a more generic approach to MSD types. Andrew (Cisco) advocated for explicitly listing known SID types for clarity and interoperability while allowing for future extensions.
B-SID Extensions in PCEP:
- Samuel (Cisco) presented extensions to RFC 9604, proposing to relax the current requirement to reject LSP requests if a binding SID is unavailable, instead allowing creation in a "down" state.
- Also proposed dynamic fallback to a PCE-allocated B-SID if the requested one is unavailable. New flags (D-flag for down state, F-flag for fallback, A-flag for allocated/requested indication) were introduced.
Multi-Path Support in PCEP:
- Samuel (Cisco) introduced a draft for multiple segments/paths per LSP (e.g., ECMP, bandwidth splitting), Reverse LSP (REL) encoding, and protection between segment lists (specifically for point-to-multipoint).
- Discussion centered on whether the proposed "backup" functionality for segment lists aligns with the SR policy architecture, which typically defines segment lists for weighted load balancing, not active/backup. Andrew and Humen clarified that this functionality is primarily intended for point-to-multipoint SR policies, particularly in environments without an underlying IGP for protection.
PCEP Extension for Deterministic Latency:
- John Schoong (ZTE) presented updates, including aligning metadata encoding with data plane taxonomy, redefining "Jitter" to "variation" metric, and proposing new metric types (min/max/variation latency).
- A D-flag for requesting deterministic paths and DPR_ERO/RRO sub-objects for carrying deterministic latency information (aligned with DatNet taxonomy) were proposed.
- Adnan (individual) noted that this is an individual contribution and not yet a DatNet WG consensus document, recommending coordination with the DatNet WG.
BFD Extensions in PCEP:
- Marina (Libon Communication) presented updates, including fixing multiplier ranges, adding a Traffic Type bit string for SBFD capability, and defining the discriminator as a mandatory TLV when SBFD is enabled.
- Zaffer suggested an explicit statement that Profile ID can be used for BFD configuration.
- A discussion occurred on the utility of signaling BFD capability per specific traffic type (e.g., SRv6, SR-MPLS, R-SPPT). Andrew argued for its usefulness in autonomous functions and mixed networks where PC-initiated LSPs might need to adapt to varying node capabilities.
PCE Redundancy:
- Marina (Libon Communication) introduced a draft addressing the problem of orphaned LSPs when an active PCE session terminates, as existing mechanisms for a standby PCE to take over are often insufficient or interoperability-challenged.
- The proposed high-level solution involves PCC providing delegation information to all active PCEs and sending notifications upon delegation timer expiry to trigger a standby PCE to take ownership.
- Samuel (Cisco) supported the problem statement, noting interoperability issues with existing re-delegation mechanisms. The chairs requested further clarification on why existing mechanisms (e.g., state synchronization) are insufficient.
LSP Creation in Down State:
- Marina (Libon Communication) presented a draft proposing a generic mechanism to allow LSPs to be established in a "down" state if initial validation fails, with the expectation that the problem might be temporary and resolve later. This would be indicated by a D_CAPABILITY flag and specific bit string for different use cases.
PCEP Extension for Precision Metrics:
- Luis (Telefonica) provided an update, noting receipt of comments from the TEAS WG. An appendix on histogram building for different metric types was added. Rakesh Kandhi (Cisco) requested more explanation on how to use the metric for path computation. The draft is seeing good reception across IPPN, DETNET, and TEAS.

Decisions and Action Items

Rakesh Kandhi to post the Auto-Bandwidth update (extending to SR) to the mailing list for feedback.
Authors of the SRv6 MSD Limitations draft to discuss consolidating their work with other MSD-related drafts (e.g., agency SID draft) and initiate a mailing list discussion on generic vs. specific MSD type representation.
Authors of the Multi-Path Support in PCEP draft to explicitly mention in the document that backup/opposite direction functionality is specific to Point-to-Multipoint SR policies to clarify its scope.
Authors of the PCE Redundancy draft to further clarify the problem statement, specifically detailing why existing mechanisms (e.g., state synchronization) are insufficient, and to seek further feedback on the mailing list before focusing on solution details.

Next Steps

The SR Point-to-Multipoint Policy PCEP draft is expected to move into Working Group Last Call soon.
The Deterministic Latency draft will continue to be reviewed, with coordination with the DatNet Working Group planned before adoption.
Discussions on BFD Extensions, including the use of Profile ID and the granularity of capability signaling, will continue on the mailing list.
The PCE Redundancy and LSP Creation in Down State drafts will seek further feedback from the working group on the mailing list to validate the problems and proposed approaches.
The Precision Metrics draft will address comments received from the TEAS WG and then seek working group adoption.
The chairs will review the working group's Last Call and adoption queues following the meeting to update the wiki.