Markdown Version | Session Recording

Session Date/Time: 11 Nov 2021 14:30

bier

Summary

The BIER working group met to discuss the status of several drafts, including mldp-bier-v2, pce-based-bier, and slicing-traffic-differentiation. A new draft proposing a "Recursive Bitstring Structure" for BIER was also presented, aiming to simplify BIER-TE complexity. The group noted concerns about the slow pace of progress due to low mailing list activity and discussed the need for an interim meeting. The chair provided an update on isis-bier-te's ISG review. Discussions also covered te-lan-bfr and bier-protection drafts.

Key Discussion Points

• Meeting Logistics: Tony volunteered to take minutes. The chair clarified the process for collaborative note-taking via the shared notepad and jabber logs.
• Working Group Pace: Concerns were raised regarding the slow progress of drafts due to limited mailing list activity and short meeting slots. Alvaro suggested scheduling an interim meeting.
• Dependency on BIER Ping: Human highlighted that the BIER Ping document has expired, blocking progress on Path MTU Discovery in BIER.
• draft-ietf-bier-mldp-bier-v2 (Human):
  • Aims to facilitate incremental upgrades from MPLS LDP multicast (MLDP) to BIER without extensive software or configuration changes.
  • Leverages RFC 7060, T-LDP between BIER edge routers for FEC signaling.
  • Discussion points included ensuring proper cross-WG visibility (MPLS, BESS) during Working Group Last Call (WGLC).
  • The draft was incorrectly marked as "informational" and lacked normative references, requiring correction.
• draft-ietf-bier-pce-based-bier (Juan Ali):
  • Introduced updates to PCE objects for BIER, defining new TLVs for multicast source/group addresses, VPN information (RD, forwarding label), and BIER information (router ID, subdomain ID, BF RID, BSL).
  • Discussion included suggestions for a more precise document title and questions about the handling of "non-BIER" scenarios within BIER-specific objects. Torless suggested broadening the scope to a general BIER PCE architecture beyond just IP multicast.
• draft-ietf-bier-slicing-traffic-differentiation (Jeffrey):
  • Explored methods for network slicing and traffic differentiation in BIER.
  • Proposed mapping slice aggregates (SAs) to BIER subdomains or directly to BIER Routing Tables (BIRT) for scalability, requiring IGP/BGP extensions.
  • Suggested a "BIER Extension Header" to carry slice selectors for finer-grained traffic differentiation, aligning with similar concepts in IPv6 and MPLS for generic delivery functions and stateless QoS.
  • Discussion touched upon the relationship with flex-algo and IPA drafts, which address similar slicing concepts.
• draft-ietf-bier-isis-bier-te (Torless):
  • Status update: ISG review completed in August, with one DISCUSS point (a typo) and numerous comments.
  • The author is working on version -11, addressing feedback, including clarifying terminology (e.g., "BIER," "non-TE BIER," "BIER-TE").
• draft-wibg-bier-rbs (Torless):
  • Proposed "Recursive Bitstring Structure (RBS)" to address complexities and scalability limitations of BIER-TE's flat bit strings, particularly for sparse multicast trees.
  • RBS structures the bit string to reflect the distribution tree, with "recursive units" extracted and rewritten at each hop, simplifying controller logic and reducing state on BFRs.
  • The forwarding plane would incur some additional processing for address rewriting.
  • Packet encoding could potentially use RFC 8296 as a new BIFT mode.
  • The chair confirmed this work is within the BIER WG charter.
• draft-chen-bier-te-lan-bfr (Chen Liya):
  • Addressed potential duplicate packets on broadcast links (LANs) in existing BIER-TE.
  • Proposed introducing "pursuit nodes" and having real nodes act as proxies, managing two forwarding tables.
  • The problem statement regarding duplicates was questioned, suggesting it might stem from sub-optimal mask generation by the PCE.
• draft-chen-bier-protection (Chen Liya):
  • Extended BIER protection mechanisms to cover "Case B," where a backup node protects a primary node, but they send packets to different CE receivers (unlike "Case A," where they send to the same receivers).
  • Utilizes a flag (s=0) to indicate different CE receivers and requires BFRs to extend forwarding tables with backup entries.

Decisions and Action Items

• General:
  • Tony volunteered as the minute taker for this session.
  • The chairs will coordinate an interim meeting, targeting mid-late January, to address the backlog of documents and foster more active discussion.
  • The chair will review the status of all current BIER documents and communicate updates on the mailing list, particularly for the expired BIER Ping draft.
• draft-ietf-bier-mldp-bier-v2:
  • ACTION: Human to correct the draft's status to "standards track" and add necessary normative references.
  • ACTION: Chairs to coordinate with Human to send WGLC notification emails to the MPLS and BESS working groups when the WGLC begins.
• draft-ietf-bier-pce-based-bier:
  • ACTION: Juan Ali to clarify the purpose of the "known beer" flag on the mailing list and consider expanding the draft's scope to a more general BIER PCE architecture.
• draft-ietf-bier-slicing-traffic-differentiation:
  • ACTION: Jeffrey to review flex-algo and IPA drafts to understand their relationship and potential synergy.
  • ACTION: Jeffrey to initiate a discussion on BIER extension headers within the BIER working group for broader generic delivery functions and stateless QoS.
• draft-ietf-bier-isis-bier-te:
  • ACTION: Torless to submit v-11 addressing ISG review comments, including clarifying terminology.
• draft-chen-bier-te-lan-bfr:
  • ACTION: Chen Liya to provide further clarification on the problem statement (duplicate packets on broadcast links) and solution details on the mailing list.
• draft-chen-bier-protection:
  • ACTION: Chen Liya to clarify the use cases and the relationship between "Case A" and "Case B" for BIER protection on the mailing list.

Next Steps

• The working group will focus on increasing activity on the mailing list to facilitate discussion and document review.
• An interim meeting will be scheduled for mid-to-late January.
• Authors are encouraged to progress their drafts and address identified action items, particularly those related to WGLC and ISG review.
• Further discussions on new concepts like BIER Extension Headers and Recursive Bitstring Structure are expected.