Session Date/Time: 27 Feb 2024 14:00

SNAC

Summary

The SNAC working group held an interim meeting to review open Pull Requests (PRs) and discuss outstanding technical issues. Key discussions included the status of the Stub Router Flags document, clarifications on prefix terminology, the handling of Router Advertisement (RA) M/O bits and associated timers, the strategy for IANA allocation of a new RA flag bit, and the implications of the L-bit on various Layer 2 networks. Several PRs were approved for merging, with some requiring minor adjustments or further work in new issues. The group outlined next steps for document progression towards IETF 119, including publishing an updated draft and continuing interim meetings.

Key Discussion Points

Stub Router Flags Document: The document is currently expired. The working group agreed on the importance of the stub router bit for SNAC functionality to prevent instability. There was a discussion about the confidence in the proposed early bit allocation and the need to expedite the process to prevent conflicts with other allocations.
ULA Prefix Terminology: Extensive discussion occurred regarding the use of "ULA site prefix," "ULA link prefix," and "onlink prefix." Concerns were raised about the ambiguity of "ULA link prefix" in certain contexts and its applicability to the Nat64 prefix, which is never truly "on-link." The importance of precise terminology for developers and clarity in an unmanaged network context was emphasized.
Router Advertisement (RA) M/O Bits and Timers: The group discussed the mechanism for reflecting M and O bits from infrastructure RAs. A key point of contention was the duration for which these bits should be reflected, particularly when the source RA becomes "stale." Concerns were raised about using stale RA time (10 minutes) as it might be too short, leading to "thrashing" of M/O bits. A longer, potentially 30-minute, duration was suggested, aligning with previous V6 Ops discussions (Fernando Gont's work) on router lifetime adjustments to balance responsiveness with stability. The practical implications of sustained M/O bits (e.g., during complex reboot scenarios) were also considered, with the conclusion that it might not cause interop problems but deviates from reflecting operator intent.
RA Flag Bit Allocation Strategy: The document currently refers to a router advertisement header Flags field. Discussion revolved around requesting an IANA allocation for an existing spare bit (e.g., bit 6 or 7) in the main RA header versus using the RA Flags Extensions Option (bits 8-55). While the extension option offers more flexibility for early allocation, there were historical concerns about older implementations failing to parse unknown RA options. The group decided to first request one of the remaining bits in the main header from 6MAN, and if rejected, then pursue the extension option.
L-bit Setting on Adjacent Infrastructure Link (AIL): A detailed discussion highlighted that explicitly setting the L-bit in RAs on the AIL, implying on-link determination and Neighbor Discovery (ND) capability, might not be universally appropriate for all Layer 2 network types (e.g., some Wi-Fi systems that isolate client traffic or non-broadcast multi-access networks). This exposes a potential gap in existing RFCs (like 4861) for unmanaged networks.
Client Mobility (RFC 8734) and PD per Host: The implications of Prefix Delegation (PD) per host (RFC 8734) were discussed. If no prefixes are available via PD, the stub router should fall back to a self-generated prefix. It was also noted that if PD per host is enabled on the AIL, it indicates IPv6 support, which could influence the stub router's decision to advertise its own prefix.

Decisions and Action Items

Decisions:

Stub Router Flags Document: The working group will request an early IANA allocation for the stub router flag bit.
PR Merges:
- The PR for ula-site-prefix (https://github.com/ietf-wg-snac/draft-ietf-snac-architecture/pull/XX - assumed to be the one discussed as ready to go at 00:12:00) is approved for merging.
- The PR changing "usable" to "suitable" (https://github.com/ietf-wg-snac/draft-ietf-snac-architecture/pull/XX - assumed to be the one discussed at 00:30:01) is approved for merging.
- Make file changes PR (https://github.com/ietf-wg-snac/draft-ietf-snac-architecture/pull/XX - assumed to be the one discussed at 00:30:57) is approved for merging.
- The PR adding requirement for no default route (https://github.com/ietf-wg-snac/draft-ietf-snac-architecture/pull/XX - assumed to be the one discussed at 01:08:08) is approved for merging, contingent on typo correction.
- The PR for Type C hosts (https://github.com/ietf-wg-snac/draft-ietf-snac-architecture/pull/XX - assumed to be the one discussed at 01:10:04) is approved for merging.
RA Flag Bit Allocation: The working group will proceed with asking 6MAN for allocation of existing bits 6 or 7 in the IPv6 ND Router Advertisement Flags field.
Terminology: The section title "Glossary" in the document will be changed to "Terminology." The term "node" will be added to the terminology section.
Capitalization: A sense of those present indicates a preference to reduce unnecessary capitalization for defined terms (e.g., "ula link prefix" instead of "ULA Link Prefix"), unless they are acronyms.
L-bit Clarification: Text will be added to the document stating, "The L-bit may not be appropriate for some Layer 2 implementations; the exact handling of such situations is out of scope for this document." This issue will also be raised with 6MAN.

Action Items:

Chairs: Initiate a SNAC working group Last Call for the Stub Router Flags document to allow for internal review before sending it to 6MAN.
Jonathan: Update the PR related to "Generating a per-router ULA site prefix" to incorporate language clarifications, including addressing the ambiguity of "ULA link prefix" versus "onlink prefix" and modifying "derived from" to "allocated from" in the glossary definition. Any remaining complex changes should be raised as new issues.
Jonathan: Beef up the Stub Router Flags draft with more justification and text in preparation for the IANA allocation request to 6MAN.
Kieran: Write a Pull Request to add an appendix to the document detailing all Router Advertisement bits and timers, including their motivation, as discussed for Issue 36.
Ted: Review the last interim meeting's recording to capture the specific text suggested for Nat64 and create a new Pull Request to incorporate it.
All PR Authors: Finalize and merge all approved Pull Requests quickly, addressing any outstanding minor comments.
Jonathan/Esco/Ted (Volunteers): Publish the current version of the document from the repository by Monday morning, UTC, to meet the IETF 119 document submission deadline.
Working Group: Update the document's text regarding "suitable prefixes" to account for scenarios involving Prefix Delegation per Host (RFC 8734), which may require a new Pull Request.
Working Group: Familiarize themselves with all remaining open issues to prepare for in-depth discussion and resolution at IETF 119.

Next Steps

Pre-IETF 119: All approved Pull Requests will be merged, and an updated draft will be published for IETF 119. The SNAC WG Last Call for the Stub Router Flags document will be initiated.
IETF 119 Meeting: The meeting will focus on reviewing changes in the updated draft, discussing remaining open issues, and planning future work.
Post-IETF 119: The working group will continue to hold interim meetings (proposed every 2-3 weeks) to maintain momentum and make progress on the document.
Future Documents: Further work on the managed use case document, which is part of the SNAC charter, will be pursued.
IETF Liaison: A formal request for IANA allocation of the Stub Router Flag bit will be submitted to 6MAN. The L-bit applicability on Layer 2 networks issue will also be raised with 6MAN.