eBGP Update-source & multihop

  • Local router find the outgoing interface for the neighbor
  • the IP of the outgoing interface is used as the source IP by default.
  • With one link a failure in that link can lose the neighborship.
    • ┬áconfigure two neighbor commands
    • Use the loopback interfaces as TCP endpoints
  • Loopback links between two AS might miss the route to the peer’s loopback
    • fixed with multihop (TTL=255 instead of TTL=1).

      • create routes between peers to reach loopback address.
      • configure update-source so the right source-ip is used.
R10#(config)router bgp 10
R10#(config-router)neighbor remote-as 20
R10#(config-router)neighbor ebgp-multihop
R10#(config-router)neighbor update-source loopback0

R20#(config)router bgp 20
R20#(config-router)neighbor remote-as 10
R20#(config-router)neighbor ebgp-multihop
R20#(config-router)neighbor update-source loopback0

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