[c-nsp] Redistribution BGP/OSPF best practice

[Oliver Boehmer (oboehmer)]

Nathan <mailto:have.an.email at gmail.com> wrote on Monday, February 25,
2008 10:42 AM:

 
> 
>>  > > and OSPF? I redistribute some internal routes between BGP and
>>  OSPF, > > but the why and the "how to avoid" of that is a story in
>> itself. 
> 
> This problem is coming back to bite me again. I have routers in
> different datacenters, all interconnected by iBGP, and clients
> connected to different datacenters using my IPs, with private AS eBGP
> for redundancy. When I privilege one link, I set either
> local-preference on my side, or (preferably) MED on the client side.
> When I do not privilege one link, I want the backbone OSPF cost to
> determine what link is used. Using BGP only it doesn't happen that
> way, because BGP does not know what exit router is nearest. 

BGP should be able to tell, shortest IGP distance is one step within the
decision step. How is the BGP next-hop being advertised/seen in your
OSPF? If you use loopbacks for your iBGP, configured next-hop-self and
advertised the loopbacks as internal routes, every iBGP speaker should
use the shortest exit ("hot potato"). If you advertised the BGP next-hop
as external-2, you could run into this situation as OSPF doesn't
consider the internal cost to the ASBR.. Could this be your issue?

 	oli