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OSPF Hybrid Broadcast and P2MP Interface Type

This document outlines the implementation of a hybrid interface type in OSPF designed for broadcast networks, particularly in scenarios where different metrics exist among neighbors, such as in wireless or wired Ethernet environments. The hybrid interface treats neighbor discovery, adjacency, and database synchronization as broadcast processes while handling Link State Advertisements (LSAs) as point-to-multipoint (P2MP). Key topics include metrics configuration, scalability, graceful restart considerations, and compatibility requirements among routers to prevent traffic issues and maintain efficient DB synchronization.

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OSPF Hybrid Broadcast and P2MP Interface Type

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  1. OSPF Hybrid Broadcast and P2MP Interface Type draft-nsheth-ospf-hybrid-bcast-and-p2mp-01.txt 79th IETF, Beijing Nischal Sheth Lili Wang Jeffrey Zhang

  2. Problem Statement Broadcast Network but with different metrics between different neighbors Wireless broadcast network where some stations may have less-optimal placement Wired Ethernet where routers have different interface speeds Want to take advantage of the broadcast property Neighbor discovery & maintenance via multicast hello Adjacencies with DR/BDR only DB Synchronization, flooding via DR/BDR 8 R1 R2 15 12 8 10 5 R3 R4

  3. Solution: Broadcast-p2mp hybrid interface • Treat as broadcast for: • Hello, adjacency, DB synchronization and flooding • Treat as p2mp for LSAs: • Details in section 3.6 • No Network LSA • Individual p2p links in Router LSA • Metrics can be either statically configured per-nbr, or dynamically learned if the underlying network supports it • Treat as p2mp for nexthop calculation

  4. Special Considerations • Graceful Restart • Some straightforward additional considerations in section 3.8 • Compatibility • All routers connected by the hybrid interface need to support it • Otherwise • No traffic traversing certain pairs of routers • No persistent traffic loops or blackhole, though • Could use Link Local Signaling to signal the hybrid support and prevent adjacency from forming if there is inconsistency • Could use LLS to signal local interface speed for others to figure out metrics automatically • if speed is the only factor leading to per-nbr metrics • Scalability • O(N^2) links (comparable with p2mp) vs. O(N) (with broadcast)

  5. Next Step? • Same concept could be used for TE • Do we care about NBMA-p2mp-hybrid? • Saves on adjacencies & DB sync/flooding • Not on hello • WG work item -> proposed standard ? • Individual submission for Informational/BCP RFC?

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