BGP next-hop

Ingo Flaschberger if at xip.at
Thu Sep 30 17:01:10 CDT 2010


> i was recently bitten by a cousin of this
>
> research router getting an ebgp multi-hop full feed from 147.28.0.1
> (address is relevant)
>
> it is on a lan with a default gateway 42.666.77.11 (address not
> relevant), so it has
>
>    ip route 0.0.0.0  0.0.0.0  42.666.77.11
>
> massive flapping results.
>
> it seems it gets the bgp route for 147.28.0.0/16 and then can not
> resolve the next hop.  it would not recurse to the default exit.
>
> of course it was solved by
>
>    ip route 147.28.0.0  255.255.0.0  42.666.77.11
>
> but i do not really understand in my heart why i needed to do this.

last time severall years ago on cisco I used a route-map to rewrite the 
next-hop.
route-map xx-in permit 10
  set ip next-hop 42.666.77.11
route-map xx-out permit 10
  set ip next-hop x.x.x.x

  neighbor 147.28.0.1 remote-as yyy
  neighbor 147.28.0.1 ebgp-multihop 8
  neighbor 147.28.0.1 route-map xx-in in
  neighbor 147.28.0.1 route-map xx-out out

something like this.







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