That's the correct behavior for BGP in the newer versions of IOS, a iBGP peer will withdraw its route if it learns it's iBGP peer has a better path. The result is you will see iBGP peer with less routes than you would expect (assuming that's what you're referring to below).
Brian [EMAIL PROTECTED] wrote: >Folks, > >I am very interested in the conclusion of this thread, but I do not have the >time to decipher it. Could somebody please summarize. > > >W. Alan Robertson wrote: > >>Well, that's exactly what I'm seeing, but it certainly wasn't what I >>expected. Nor did it appear to be what our TAC engineer expected... >>I'm going to get the case notes in the morning, and I'll share them >>with the list. >> >>Thanks for mocking this up Przemek... Now if you can manage to get >>that config time down to 20 minutes, instead of an hour, you're going >>to kick butt in the Lab. ;) >> >>----- Original Message ----- >>From: "Przemyslaw Karwasiecki" >>To: "W. Alan Robertson" >>Cc: "Peter van Oene" ; "Groupstudy - CCIELAB" >>; "Groupstudy - Cisco Certification" >> >>Sent: Tuesday, February 05, 2002 10:50 PM >>Subject: Re: Undocumented iBGP Behavior (Confirmed by Cisco) >> >>>I have prepended it in the router in AS3. >>> >>>I wanted to simulate longer paths from one of the ASes, >>>like it happens between AS1 and AS 701 in reality. >>> >>>Main point I wanted to prove is that initialy both routers >>>have all routes, but after BGP converged, righ router (r6) >>>selected routes learned via iBPG from r5, and withdrawn >>>routes via AS3 from its advertisments to left router (r5). >>> >>>Przemek >>> >>> >>>On Tue, 2002-02-05 at 22:40, W. Alan Robertson wrote: >>> >>>>How are you ending up with a greater number of AS hops for the >>>> >>route >> >>>>on R6 learned via AS3? >>>> >>>>>r6#sh ip bgp 10.0.0.0 >>>>>BGP routing table entry for 10.0.0.0/8, version 3 >>>>>Paths: (2 available, best #2, table Default-IP-Routing-Table) >>>>> Advertised to non peer-group peers: >>>>> 1.1.34.3 >>>>> 3 3 1 >>>>> >>>> ^^^ >>>> | Why does there seem to be an as-prepend here? --Alan >>>> >>>>> 1.1.34.3 from 1.1.34.3 (1.1.34.3) >>>>> Origin IGP, localpref 100, valid, external >>>>> 2 1 >>>>> 1.1.24.2 from 2.2.2.1 (2.2.2.1) >>>>> Origin IGP, localpref 100, valid, internal, best >>>>> >>>>Again, in this case, the iBGP learned route is preferred because >>>> >>it is >> >>>>only two AS hops away... The externally learned route, from peer >>>>1.1.34.3, shows AS3 twice in the path, making this route 3 AS hops >>>>away. >>>> >>>> >>>>----- Original Message ----- >>>>From: "Przemyslaw Karwasiecki" >>>>To: "W. Alan Robertson" >>>>Cc: "Peter van Oene" ; "Groupstudy - CCIELAB" >>>>; "Groupstudy - Cisco Certification" >>>> >>>>Sent: Tuesday, February 05, 2002 10:15 PM >>>>Subject: Re: Undocumented iBGP Behavior (Confirmed by Cisco) >>>> >>>> >>>>>Ok, >>>>> >>>>>Lab is done. I expected 20 minutes, it tooks 1 hour. >>>>>Important lesson about time management learnt :) >>>>> >>>>>small legend: >>>>>r5 and r6 are routers in AS4 >>>>> >>>>>If anyone care I can send complete configs. >>>>> >>>>>Przemek >>>>> >>>>>r5#sh ip bgp summ >>>>>BGP router identifier 2.2.2.1, local AS number 4 >>>>>BGP table version is 2, main routing table version 2 >>>>>1 network entries and 1 paths using 133 bytes of memory >>>>>1 BGP path attribute entries using 60 bytes of memory >>>>>1 BGP AS-PATH entries using 24 bytes of memory >>>>>0 BGP route-map cache entries using 0 bytes of memory >>>>>0 BGP filter-list cache entries using 0 bytes of memory >>>>>BGP activity 1/9 prefixes, 2/1 paths, scan interval 60 secs >>>>> >>>>>Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ >>>>> >>Up/Down >> >>>>State/PfxRcd >>>> >>>>>1.1.24.2 4 2 23 22 2 0 0 >>>>> >>00:18:14 >> >>>>1 >>>> >>>>>2.2.2.2 4 4 27 26 2 0 0 >>>>> >>00:21:53 >> >>>>0 >>>> >>>>>r5#sh ip bgp 10.0.0.0 >>>>>BGP routing table entry for 10.0.0.0/8, version 2 >>>>>Paths: (1 available, best #1, table Default-IP-Routing-Table) >>>>> Advertised to non peer-group peers: >>>>> 2.2.2.2 >>>>> 2 1 >>>>> 1.1.24.2 from 1.1.24.2 (1.1.1.1) >>>>> Origin IGP, localpref 100, valid, external, best >>>>>r5# >>>>>telnet-server#6 >>>>>[Resuming connection 6 to r6 ... ] >>>>> >>>>>r6#sh ip bgp summ >>>>>BGP router identifier 2.2.2.2, local AS number 4 >>>>>BGP table version is 3, main routing table version 3 >>>>>1 network entries and 2 paths using 169 bytes of memory >>>>>2 BGP path attribute entries using 120 bytes of memory >>>>>2 BGP AS-PATH entries using 48 bytes of memory >>>>>0 BGP route-map cache entries using 0 bytes of memory >>>>>0 BGP filter-list cache entries using 0 bytes of memory >>>>>BGP activity 1/6 prefixes, 2/0 paths, scan interval 60 secs >>>>> >>>>>Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ >>>>> >>Up/Down >> >>>>State/PfxRcd >>>> >>>>>1.1.34.3 4 3 21 20 3 0 0 >>>>> >>00:15:20 >> >>>>1 >>>> >>>>>2.2.2.1 4 4 27 28 3 0 0 >>>>> >>00:22:13 >> >>>>1 >>>> >>>>>r6#sh ip bgp 10.0.0.0 >>>>>BGP routing table entry for 10.0.0.0/8, version 3 >>>>>Paths: (2 available, best #2, table Default-IP-Routing-Table) >>>>> Advertised to non peer-group peers: >>>>> 1.1.34.3 >>>>> 3 3 1 >>>>> 1.1.34.3 from 1.1.34.3 (1.1.34.3) >>>>> Origin IGP, localpref 100, valid, external >>>>> 2 1 >>>>> 1.1.24.2 from 2.2.2.1 (2.2.2.1) >>>>> Origin IGP, localpref 100, valid, internal, best >>>>>r6# >>>>> >>>>> >>>>>Once better route is selected in Local-RIB, the other, >>>>>previously advertised is withdrawn. >>>>> >>>>> >>>>> >>>>>On Tue, 2002-02-05 at 21:15, W. Alan Robertson wrote: >>>>> >>>>>>If you can, build your test scenario to look like this: >>>>>> >>>>>> >>>>>> [eBGP ] >>>>>> ___[AS 1]___ >>>>>> | | >>>>>> | | >>>>>> [ eBGP ] [ eBGP ] >>>>>> [ AS 2 ] [ AS 3 ] >>>>>> | | >>>>>> | | >>>>>> | | >>>>>> | | >>>>>> [ BGP ] [ BGP ] >>>>>> [ AS 4 ] [ AS 4 ] >>>>>> | | >>>>>> | | >>>>>> _|___________|_ >>>>>> >>>>>> >>>>>>Originate a route (say the 10.0.0.0/8 route) in AS 1, and see >>>>>> >>what >> >>>>>>happens in AS 4. >>>>>> >>>>>>You should see two entries for the 10/8 network in 'show ip >>>>>> >>bgp' >> >>>>>>output, one of which is learned via the eBGP peer, and gets >>>>>> >>>>installed >>>> >>>>>>in your routing table, and the second, learned via the iBGP >>>>>> >>peer, >> >>>>>>which does not get installed in your routing table. >>>>>> >>>>>>That is the time-honored behavior, the behavior we've all come >>>>>> >>to >> >>>>know >>>> >>>>>>and love since the dawn of time, etc, etc, amen. :) >>>>>> >>>>>>Now, in 12.0(20), this behavior is changed to they behavior I >>>>>> >>have >> >>>>>>described in this thread. I don't know when this change >>>>>> >>occurred, >> >>>>but >>>> >>>>>>hope to have that question answered tomorrow. Most of my >>>>>> >>other >> >>>>BGP >>>> >>>>>>customers are running 12.1 stuff... >>>>>> >>_________________________________________________________________ >>CCIE Security list: http://www.groupstudy.com/list/security.html >> >_________________________________________________________________ >Commercial lab list: http://www.groupstudy.com/list/commercial.html >Please discuss commercial lab solutions on this list. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38616&t=38616 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
