08-12-2004 05:28 PM - edited 03-02-2019 05:44 PM
Hi,
A question for the Cisco insiders, I guess..
Here's an excerpt from the KnowledgeNet BGP 3.0 course:
"Only the route selected as best is propagated to the neighbors. However, a route is never sent back on the same BGP session that it was received. On the contrary, when a neighbor is selected, the best next-hop, the local router, makes sure that the neighbor is not pointing back to the local router by poisoning the route and sending a withdraw message to that neighbor.
This is to avoid a potential routing loop problem where the neighbor router selected as the best next-hop relies on the local router as the best next-hop."
I have not seen evidence of such "poisoned" routes being sent in my testing. Is this possibly something that used to happen on older IOSs ?
All help appreciated.
Regards,
Paresh.
Solved! Go to Solution.
08-12-2004 05:59 PM
The BGP poisoned reverse should ocur under the following circumstances.
router A advertises route X to router B and all of a sudden router B starts advertising route X to router A and router A selects it as a best path, router A sends back a withdrawal message to router B.
If you test this exact scenario you should see the withdrawal message.
Hope this helps,
08-12-2004 05:59 PM
The BGP poisoned reverse should ocur under the following circumstances.
router A advertises route X to router B and all of a sudden router B starts advertising route X to router A and router A selects it as a best path, router A sends back a withdrawal message to router B.
If you test this exact scenario you should see the withdrawal message.
Hope this helps,
08-12-2004 06:36 PM
Thanks, that does help.
Paresh
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