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OSPF Two-part Metrics

OSPF Two-part Metrics. Jeffrey Zhang Lili Wang Juniper Networks 88 th IETF, Vancouver. RFC 6845 Hybrid Interface. A broadcast network with different costs between different pairs of neighbors Treat as broadcast for Hello, adjacency and database synchronization purpose

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OSPF Two-part Metrics

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  1. OSPF Two-part Metrics Jeffrey Zhang Lili Wang Juniper Networks 88th IETF, Vancouver

  2. RFC 6845 Hybrid Interface • A broadcast network with different costs between different pairs of neighbors • Treat as broadcast for Hello, adjacency and database synchronization purpose • Treat as p2mp to advertise different costs for different neighbors

  3. Hybrid interface limitations • Each Router LSA has N-1 links for the interface • One for each neighbor • In some networks, e.g. a satellite radio based one, the change in one router’s communication capability causes all attached routers to update their Router LSAs • This causes unbearable flooding in a large network with routers constantly moving around

  4. Observation 1 • In the example satellite radio network, if one router’s communication capability changes, all costs change in a similar fashion: • other routers’ cost to it • its cost to all other routers R1 R2 R3 R1->R2: 10 R1->R3: 20 R2->R1: 15 R2->R3: 25 R3->R1: 20 R3->R2: 25 + 150 + 150 + 100 + 100

  5. Observation 2 • Network LSA does not have costs associated with listed routers • It is assumed that a router’s cost to all neighbors are the same • encoded in the transit link in Router LSA • Note that different routers can still encode different costs in the transit link of their own Router LSA for the same network Router LSA for R1 V1 V2 Transit link in R1’s Router LSA 15 20 W 30 Net LSA V3 Router LSA for R2 Router LSA for R3 SPF calculation result: R1->R2,R3: cost 15 R2->R1,R3: cost 20 R3->R1,R2: cost 30

  6. Proposed solution • Use Router and Net LSAs instead of advertising p2p links • Break router to router cost to two parts: to/from-network • Advertise both in the transit link (of a different type X) • For OSPFv2, encode from-network cost as an MT cost • For OSPFv3, use TLV per draft-acee-ospfv3-lsa-extend • Network LSA as is • SPF calculation to consider both to- and from-network costs • When one router’s communication capability changes, only its own Router LSA is updated Router LSA for R1 5 10 10 10 V1 V2 W 15 20 Net LSA V3 Router LSA for R2 Router LSA for R3 R1->R2: 10+10=20 R1->R3: 10+15=25 R2->R1: 10+5 =15 R2->R3: 10+15=25 R3->R1: 20+5 =25 R3->R2: 20+10=30

  7. Plan • Seeking review & comments • Polish the solution • Finish OSPFv3 TLV details • Advertising a router’s support for this? • If one router does not support this extension, all from-network costs are treated as 0 • Seeking WG adoption

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