Wednesday, December 3, 2008

BGP Next Hop

With iBGP the next hop for the advertised route is changed to match the address of the advertising router.

With eBGP the next hop is unchanged based on the assumption that the receiving router must have reachability to the eBGP peer address. If this assumption is incorrect there are a number of commands that can be used to manipulate the next hop address associated with the route.

The simplest of these is
neighbor a.b.c.d next-hop-self

This will change the next hop for all advertised routes to the local router address.

If more garnularity is required or you are prohibited from using 'next-hop-self' then route maps can be used to influence the next hop of advertised routes.

route-map TO_R4
set ip next-hop peer-address

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