From: Vikram Dadlaney (vdadlaney@gmail.com)
Date: Tue May 16 2006 - 12:40:29 ART
Arun,
Just a guess over here but when the EBGP route is selected as the best route
I assume it would be installed in the Routing Table since Admin distance is
20. Now when you bring up the IBGP neighbor with sync enabled it could be
that your route might be showing up as not synchronized since there is no
matching IGP route. Just a guess over here. Please let me know if this makes
sense. Thanks
On 5/16/06, Arun Arumuganainar <aarumuga@hotmail.com> wrote:
>
> I have a interesting BGP route selection problem . It would be great if
> any
> body can explain me this .
>
> Setup description :-
> ~~~~~~~~~~~~~~
>
> 1) I have BGP Synchronisation enabled and I am redistributing my BGP
> routes
> in to IGP . Here the IGP is RIP .
> 2) I learn a same prefix learned via two sources as follows
>
> a) First route via iBGP with Local-Pref set to 500
> b) Second one via eBGP with Local pref set to 300
>
> Actually I see route A is slected by the virtue of superior local pref
> .This
> is as expected.
>
> ****************************************
> Router Traces
> ****************************************
> R4#sh ip bgp
> BGP table version is 7, local router ID is 172.16.104.1
> Status codes: s suppressed, d damped, h history, * valid, > best, i -
> internal,
> r RIB-failure, S Stale
> Origin codes: i - IGP, e - EGP, ? - incomplete
>
> Network Next Hop Metric LocPrf Weight Path
> r 172.16.107.0/24 172.16.124.3 300 0 100 700 ?
> r>i 172.16.103.1 0 500 0 100 700 ?
> ****************************************
>
> Pls Note : Routes are tagged as 'r' as the SYNC is enabled and routes are
> also learned via IGP .
>
> Step to reproduce the problem :-
>
> I shut doen the iBGP peer using neighbor shut down command and now the
> eBGP
> routes are getting comfortably installed . as given in the router trace .
>
> ****************************************
> Router Traces
> *************************************
> R4(config-router)#neighbor 172.16.103.1 shutdown
> R4(config-router)#do sh ip bgp
> BGP table version is 9, local router ID is 172.16.104.1
> Status codes: s suppressed, d damped, h history, * valid, > best, i -
> internal,
> r RIB-failure, S Stale
> Origin codes: i - IGP, e - EGP, ? - incomplete
>
> Network Next Hop Metric LocPrf Weight Path
> *> 172.16.107.0/24 172.16.124.3 300 0 100 700 ?
>
> ****************************************
>
> Now I bring up the BGP Peer again . Now my expectation would be iBGP route
> should get re-installed right ??? But to my surprise it is not getting
> installed again.
>
>
> ****************************************
> Router Traces
> *************************************
> R4(config-router)#no neighbor 172.16.103.1 shutdown
> R4(config-router)#
> *May 16 14:16:40.449: %BGP-5-ADJCHANGE: neighbor 172.16.103.1 Up
> R4(config-router)#
> R4(config-router)#do sh ip bgp
> BGP table version is 9, local router ID is 172.16.104.1
> Status codes: s suppressed, d damped, h history, * valid, > best, i -
> internal,
> r RIB-failure, S Stale
> Origin codes: i - IGP, e - EGP, ? - incomplete
>
> Network Next Hop Metric LocPrf Weight Path
> * i172.16.107.0/24 172.16.103.1 0 500 0 100 700 ?
> *> 172.16.124.3 300 0 100 700 ?
>
> ****************************************
> To get back to old route I need to reset the peer .
>
> Just wondering if any body has seen this behaviour.
>
> Thanks and Regards
> Arun
>
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This archive was generated by hypermail 2.1.4 : Thu Jun 01 2006 - 06:33:21 ART