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Advertising ECMP Routes in BGP

Advertising ECMP Routes in BGP. Joel Halpern Manav Bhatia Paul Jakma. 65 th IETF – Dallas, TX. Requirements for an ECMP algorithm. MUST be able to advertise individual BGP paths to other multipath capable peers.

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Advertising ECMP Routes in BGP

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  1. Advertising ECMP Routes in BGP Joel Halpern Manav Bhatia Paul Jakma 65th IETF – Dallas, TX

  2. Requirements for an ECMP algorithm • MUST be able to advertise individual BGP paths to other multipath capable peers. • MUST preserve maximum path information and should be regular expression friendly • Path length MUST be retained when advertising routes to non multipath capable peers

  3. ECMP Capability • Uses MULTIPLE_HOP Capability • Defines a new bit in the bitmask of flags +-------+---+---+---+---+---+---+------+----+ | Bit: | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | +-------+---+---+---+---+---+---+------+----+ | flag: | R | R | R | R | R | R | ECMP | AE | +-------+---+---+---+---+---+---+------+----+

  4. How does this work within an AS? R1 10.0.0.0/8 AS_PATH: A B C NEXT_HOP: N2 AS 65530 10.0.0.0/8 AS_PATH: A B C MULTIPLE_HOP: N2 R3 RR 10.0.0.0/8 AS_PATH: X Y Z NEXT_HOP: N1 10.0.0.0/8 AS_PATH: X Y Z NEXT_HOP: N1 (BGP RIB) *>i 10.0.0.0/8 N2 A B C ? *>i 10.0.0.0/8 N1 X Y Z ? Assuming that R3 can reach N1 and N2 independently and not via the RR #sh ip route B 10.0.0.0 [170/0] via nexthop to the RR R2 #sh ip route B 10.0.0.0 [170/0] via N1 B 10.0.0.0 [170/0] via N1

  5. Advertising to an EBGP/non Multipath capable IBGP peer AS 61000 AS 65530 10.0.0.0/8 ORIGIN: INCOMPLETE AS_PATH: {65530} [A X] [B Y] [C Z] R3 R4 *>i 10.0.0.0/8 N2 A B C ? *>i 10.0.0.0/8 N1 X Y Z ?

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