Tricky BGP into IGP Question

Wed Jan 24 01:13:39 UTC 2001

On Tue, Jan 23, 2001 at 03:26:28PM -0800, Tim Wolfe wrote:
> 
> 
> What is the preferred way to get transit customers routing information into
> your IGP so that BGP will announce the route to it's neighbors.  
> 
> 1===2a===2b====3
>     |
>     4
> 
> 1 is the customer, announcing to 2a, who propogates 1's route to 2b and to
> 4.  2b will not announce the route to 3 as it doesn't have a route in it's
> routing table for 1's route.  I was thinking about redistributing bgp into
> my igp using a route-map based on as-path filter, but that seems somewhat
> kludgy.  What are you all doing to accomplish this or am I just missing
> something here?

Assuming each of those routers only speaks BGP to its direct neighbors
currently, I'd say the most common solutions are route reflectors (and/or
confederations) and fully-meshed BGP networks. The reason 3 doesn't see
the route is because BGP doesn't propagate routes across multiple iBGP
hops.

If one of (2a, 2b, 3, 4) acts as a route reflector, and the others peer
only with it, your route will get propagated to all of them.

Alternately, if each of (2a, 2b, 3, 4) peers with each other directly,
1 will announce to 2a and 2a will propagate to all others.

-c