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RE: Tricky BGP into IGP Question

  • From: Barry Raveendran Greene
  • Date: Tue Jan 23 21:40:17 2001

Hello Tim,

I'm assuming that "1," "3," and "4" are separate AS numbers with "2a" and
"2b" in the same as providing transit ....... given that .....

The BCP for redistributing BGP into the IGP is just _NOT_ to do it.
Redistributing BGP into the IGP is a very dangerous thing to do. Besides,
the problem you described below has nothing to do with "1" routes being in
the IGP. They should not be in the IGP in the first place. The problem you
are describing sounds just like a recursive lookup failure on "1's" next-hop

The subnet between 1 and 2a is not in the IGP. Hence, when 1's routes get to
2b, 2b will do a recursive look-up on 1's routes and have it fail (cause the
next hop is not in the forward table).

So one router 2b, check for a entry and pingability of subnet between 1 and
2a. The link between router 1 and 2a is an 'infrastructure' route, so you
want that in your IGP.


> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On Behalf Of
> Tim Wolfe
> Sent: Tuesday, January 23, 2001 3:26 PM
> To: '[email protected]'
> Subject: Tricky BGP into IGP Question
> 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?
> Thanks,
> --Tim
> =============================================
>       Timothy M. Wolfe  CCNA, NSA
>  Sr. Security Engineer  [email protected]
>    InfoGroup Northwest  541.485.0957 x108
> =============================================