From: Manny Gonzalez (gonzalu@xxxxxxx)
Date: Tue Feb 05 2002 - 19:33:33 GMT-3
Is there a STOP command? Something to let us turn that behaviour off?
The way I see it is, if the router with the 104000+ routes suddenly
dies, the other router (the one with 700 routes) has to then get all
these routes from it's remote-as peer and that could take a while (if
never, or until refreshed) Unless I missed something in your email, this
is not what would like my routers to behave like...
:-))
"W. Alan Robertson" wrote:
>
> Folks,
>
> Just to let you know, I ran across what looked like a bug in Cisco's
> BGP code... Turns out, this is undocumented new behavior.
>
> We just deployed a pair of 3640s for one of our customers, for
> dual-router, dual-homed Internet connectivity. We are taking full
> tables from Genuity (AS 1), and Worldcom (AS 701).
>
> Each router was learning 104,000+ prefixes from each of the external
> peers, but the iBGP peering was acting really strange. One of the
> routers was learning the full table from the other, but the second
> router was only taking like 700 prefixes.
>
> When we cleared the internal peer (soft or hard), we could see the
> whole table being transferred... It would climb as though it were
> going to learn them all, and then as it approached 100,000 prefixes,
> it would rapidly drop back down to 700. I debugged the iBGP peer, and
> saw it issuing withdrawls for all of these routes.
>
> We opened a ticket with the TAC, and they initially believed it to be
> a bug as well. Upon further review, they came back and told us that
> this was the desired behavior in the newer code (We are running
> 12.0(20) on these boxes). In order to conserve memory, and processor,
> if an iBGP peer learns that another iBGP peer already has a better
> route to a specific prefix, it will issue a withdrawl to that peer
> for the prefix(es).
>
> I spent quite a while second guessing what seemed to be a very simple,
> straighforward configuration. I have done several near identical
> deployments in the past.
>
> I guess the moral is this: If you know your config is correct, and
> the router behavior is not what you expect, do not hesitate to call
> the TAC.
>
> I hope they are as helpful on Monday, when I call them from the CCIE
> Lab in RTP. ;)
>
> Regards...
>
> Alan
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