BGP Reachability Question

Unanswered Question
Jun 4th, 2007
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Hey guys & gals,

I was doing one of my custom labs tonight and ran into an issue. For the life of me I can't remember the solution for this type of problem.


Scenario: Universal reachability has been achieved via the IGP's. Reachability and prefix propagation has been achieved with the exception of AS300. Prefixes are advertised as best throughout, but unreachable to AS 250, AS100. The key to this solution is R7, but what is the command to get it done?

All advertised prefixes are reachable to all AS. But only AS77 can reach the prefixes advertised by AS300.

AS300 prefixes are advertised as best in every other AS, but only reachable from AS77.

ping AS300 Prefix's from AS100 = U.U.U

ping AS300 Prefix's from AS250 = U.U.U

ping AS300 Prefix's from AS77 = !!!!!

R5 is a RR-client of R2

R5 EBGP peer with R1

R7 EBGP peer with R2

R7 EBGP Peer with R3

I know the problem is that AS77 is an EBGP peer with AS300 and doesn't know how to advertise back out to AS250 & 100.

What is the neighbor command for R7 used to get AS300 prefixes reachable to all other AS's.

I hope the picture works.


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dbdbtech001 Mon, 06/04/2007 - 19:00
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Oh, and the fix should be based on anything other than a static or default route.

CSCO10892433 Tue, 06/05/2007 - 02:54
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Hi, dbdbtech001

Interesting lab! We need more informations from you. As a first step of troubleshooting, would you please post the "show ip bgp" output on R1,R2,R3,R5, and R7 for us?



mohammedmahmoud Tue, 06/05/2007 - 03:32
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Most probably its a next-hop reachability issue, SSLIN suggestion would be nice.


Mohammed Mahmoud.


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