ahh.. so your adj rib in shows only 700 after a while?
At 07:55 PM 2/5/2002 -0500, W. Alan Robertson wrote: >Yes it does, and that would determine which of the two available >routes makes it into the actual IP routing table... It does not >explain why the router only has one BGP learned route to choose >from... > > >----- Original Message ----- >From: "Peter van Oene" >To: "Przemyslaw Karwasiecki" ; "W. Alan Robertson" > >Cc: "Groupstudy - CCIELAB" ; "Groupstudy - >Cisco Certification" >Sent: Tuesday, February 05, 2002 7:35 PM >Subject: Re: Undocumented iBGP Behavior (Confirmed by Cisco) > > > > cisco by default prefers ebgp over ibgp. it should not, by default, >enjoy > > the ibgp routes learned from the peer over the ebgp learned routes. > > > > > > > > At 05:37 PM 2/5/2002 -0500, Przemyslaw Karwasiecki wrote: > > >Correct me if I am wrong but this: > > > > > > > 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). > > > > > >is perfectly normal, standart behaviour. > > >If your Genuity route is better, you will select this route > > >in your routing table, and if by any chance before you had > > >there UUNET route which you have advertised, you need to send > > >update with new, better, selected route. > > > > > >BGP will never advertise both routes. > > >This is distant vector after all. > > > > > >So if during convergence phase your route selection > > >is shuffling your routes in your Loc-RIB, you should > > >to expect series of updates to follow up. > > > > > >Przemek > > > > > > > > >On Tue, 2002-02-05 at 16:45, 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 > > > > >_________________________________________________________________ > > > > CCIE Security list: http://www.groupstudy.com/list/security.html > > >_________________________________________________________________ > > >CCIE Security list: http://www.groupstudy.com/list/security.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=34549&t=34549 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
