Session Date/Time: 09 Nov 2021 16:00

pim

Summary

The PIM working group session at IETF 112 covered updates on numerous working group drafts, discussed a proposed charter update to formally include Point-to-Multipoint (P2MP) work, and featured presentations on LISP Join Prune extensions, PIM-Lite, IGMP/MLD extension for source management, and the advancement of IGMPv3/MLDv2 to Internet Standard. Key discussions revolved around cross-working group coordination for multicast architecture and the path forward for DR improvement drafts.

Key Discussion Points

Working Group Status Updates:
- PIM YANG Model: Publication delayed due to a bug in the BFD YANG module (RFC 9127), requiring its republication. Expectation is for publication in "weeks, not months".
- IGMP MLD Snooping YANG Model: Currently in the RFC Editor's queue.
- BFD Point-to-Multipoint Use Case: Publication evaluation requested.
- IGMP MLD Extensions: A new draft has been submitted.
- DR Improvement/Backup DR/Sticky DR: Two working group drafts exist. The chairs emphasized the need for authors to drive progress and for the working group to achieve technical agreement on the best solution (one or two) to move forward.
- IGMP MLD Proxy YANG Model: Passed working group last call, publication requested soon.
- Null Register Packing: Returned to WG previously, now reviewed and ready for publication request.
- Assert Packing: Minor comments addressed, ready for publication request.
- LISP Join Prune Extensions: Recently adopted by the WG.
- PIM Point-to-Multipoint Ping Draft: Adoption call concluded with consensus. Action item for the author to specify focus on SR-MPLS data plane and for chairs to coordinate with MPLS WG regarding code points before formal adoption.
PIM Charter Update:
- Changes: The bullet related to YANG/Management work was removed, as the YANG work is considered largely complete. A new bullet was added to formally include "develop point-to-multipoint protocols, including SR and SRv6 point-to-multipoint work per agreement with the SPRING working group." It also allows for taking on P2MP work from other working groups if requested.
- Discussion: Concerns were raised by Alvaro and June regarding the broader multicast architecture and the need for better cross-working group coordination (IDR, BESS, PCE, SPRING, etc.). A side meeting on Friday was noted for further discussion on this. Alvaro clarified that the PIM WG charter ("protocols for IP multicast") is intentionally broad to accommodate such work, but proper IETF process (charters, presentations) is required. Formalizing the charter update will await more clarity on overall multicast work coordination.
LISP Join Prune Attributes for LISP Environments using Underlay Multicast (presented by Stig Venaas):
- This adopted WG draft extends existing LISP join prune attributes to allow specifying a multicast address as a destination for LISP encapsulation, enabling underlay multicast.
- The document is considered largely complete, with the primary remaining work being security considerations.
Point-to-Multipoint Policy (presented by Hemanth Huilgol):
- Due to audio issues, the presentation was brief.
- Updates included the replication segment being adopted by SR/MPLS.
- The P2MP policy itself has been adopted by the WG.
- BESS/EVPN SR P2MP and IDR SR P2MP (BGP SRTE) drafts are progressing.
IGMP MLD Extension Source Management (SMM) (presented by Juanli):
- This draft aims to manage multicast sources and services, including access control, data flow control, and statistics. It's designed for SSM scenarios.
- Comparison with MSNP: While MSNP and this draft share the aim of controlling source behavior (e.g., minimizing traffic when no receivers), the motivations and use cases differ. This draft focuses more on authentication and controlled deployment.
- Updates: Improved multicast source registration process with timer mechanisms, extended credential length (16 bits), replaced timestamp with start time and duration, removed redundant address type fields, and added use cases (PCE-based Beer, SDN, source authentication).
- Discussion: Emphasized authentication and controlled multicast. Acknowledged the challenge of host stack upgrades for such signaling and the historical abandonment of similar "request to send" concepts. Suggestion for authors to engage more on the mailing list for detailed discussion.
PIM-Lite (presented by Hemanth Huilgol):
- This draft proposes a "lighter" version of PIM, allowing PIM Join/Prune and Assert messages without requiring PIM Hellos or full PIM adjacency.
- Limitations: No neighbor discovery, DR selection, or general-purpose state for neighboring routers.
- Use Case: Suited for networks (e.g., Beer networks) where full PIM adjacency is not optimized or desired.
- Working Group Action: As both chairs are co-authors, a volunteer shepherd is needed for adoption and working group last call. Sandy responded to volunteer for this role. Alvaro suggested renaming the draft to "PIM-Lite Interface" for clarity.
Advancing IGMPv3 and MLDv2 to Internet Standard (presented by Anleli):
- Now a working group draft, incorporating several errata and clarifications (e.g., query election process, MLD messages with link-local addresses, missing recipe field in 4773, older version query present time in 4375, editorial in 5375).
- Open Issues for WG Discussion:
  - Should RFC 1112 (IGMPv1/MLDv1) be moved to historic status?
  - Should RFC 4604 (SSM for IGMP/MLD) be incorporated, and if so, what specific text/scope?
  - How to define the relationship with new PIM IGMP MLD extension drafts (WG agrees no official update needed for these).
  - Errata 675 (Brian Haberman is addressing this).
- The co-authors were requested to send separate emails to the mailing list to outline details for these open issues to facilitate discussion.

Decisions and Action Items

PIM Point-to-Multipoint Ping Draft:
- Decision: Consensus reached for adoption.
- Action Item: Author (Hemanth Huilgol) to update the draft to explicitly specify its focus on the SR-MPLS data plane.
- Action Item: Chairs (Stig Venaas, Mike McBride) to coordinate with MPLS WG chairs regarding code point usage before formally adopting.
PIM-Lite Draft:
- Decision: Sandy (Alexey Melnikov) volunteered to act as shepherd for the draft.
- Action Item: Sandy to coordinate with chairs and authors for future progress (adoption call, WG Last Call).
- Action Item: Authors to consider renaming to "PIM-Lite Interface" based on Alvaro's suggestion.
Advancing IGMPv3 and MLDv2 to Internet Standard Draft:
- Action Item: Co-authors (Anleli) to send separate emails to the PIM mailing list to detail the proposals for:
  1. Moving RFC 1112 to historic status.
  2. Specifying the scope and text to be incorporated from RFC 4604.
Multicast and Source Routing Side Meeting:
- Action Item: Chairs to send the link to the side meeting on Friday to the PIM mailing list.

Next Steps

DR Improvement/Backup DR/Sticky DR Drafts: Authors and working group members are encouraged to engage in further discussions on the mailing list to compare approaches and agree on technical solutions to drive these drafts forward.
LISP Join Prune Attributes: Authors to work on the security considerations and solicit more working group review and comments.
IGMP MLD Extension Source Management: Continue discussions on the mailing list regarding use cases, motivations, and the scope of the draft.
PIM Charter Update: Await further cross-working group coordination and discussion on the broader multicast architecture before formalizing the charter update.
PIM-Lite: Authors to refine the draft and coordinate with the shepherd, Sandy.