[c-nsp] learned routes disappear

[Paul A]

Thanks for the reply Oli.

-----Original Message-----
From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com] 
Sent: Monday, February 09, 2009 2:32 AM
To: Paul A; Michael K. Smith - Adhost
Cc: cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] learned routes disappear

Paul,

looks like you're preferring the route from the upstream over your
customer's advertisement (for whatever reason), so it is expected that
Router B is not advertising the path received from your customer/Router
A.

You are correct: The PfxRcd counter in "show ip bgp sum" only shows the
best paths, you need to look at "show ip bgp neighbor x.x.x.x" (or "show
ip bgp neighbor x.x.x.x routes") to see all paths..

	oli


Paul A <> wrote on Sunday, February 08, 2009 00:50:

> Hi Michael,
> 
> 
> 
> it seems as I look more and more into this, mind you I'm no bgp
> expert, I think what is happening might be normal iBGP behavior. 
> 
> 
> 
> Heres how the network is setup.
> 
> 
> 
> Router A (customer) which connects to router B (my router) . Router B
> is connection to router C (my 2nd router) over iBGP. 
> 
> 
> 
> My BGP customer advertises 5 routes. The router directly connected to
> my customer's bgp router (Router A)  shows all  5 routes when I do a
> (sh ip bgp sum).  
> 
> Router C (my 2nd router iBGP) only shows these 5 router when I type
> "show ip bgp sum" for about a 1:15 to 1:30 minutes then the routes
> disappear from State/PfxRcd.  
> 
> 
> 
> When I do a show ip bgp on router B for one of the received routes
> from router A (cust router) it's says: 
> 
> 
> 
> Paths: (2 available, best #1, table Default-IP-Routing-Table)
> 
> Multipath: iBGP
> 
>   Not advertised to any peer
> 
> 
> 
> The second best route being from my customer (router A) and the 1st 
> best route being from Router C (my second iBGP router) 
> 
> 
> 
> 
> 
> Now on Router C, where I'm confused when I do show ip bgp  for the
> same route I see. 
> 
> 
> 
> Paths: (2 available, best #1, table Default-IP-Routing-Table)
> 
>   Advertised to update-groups:
> 
>      1
> 
> 
> 
> Both routes being from my two up streams on that router.
> 
> 
> 
> My confusion is when I do a show ip bgp sum <router B's neighbor
> address> I see 5 routes under State/PfxRcd then after a minute or two
> they disappear.  
> 
> 
> 
> Is this normal ibgp behavior? Are the router listed under
> State/PfxRcd only routes that are inserted in the routing table? 
> 
> 
> 
> 
> 
> From: Michael K. Smith - Adhost [mailto:mksmith at adhost.com]
> Sent: Friday, February 06, 2009 3:47 PM
> To: Paul A
> Cc: cisco-nsp at puck.nether.net
> Subject: RE: [c-nsp] learned routes disappear
> 
> 
> 
> Hello Paul:
> 
>> 
>> Paul A wrote:
>>> Hi, I'm having a bgp issue I can't figure out and hoping someone
>>> has ran into this. 
>>> 
>>> 
>>> 
>>> I have two routers, router A and router B doing bgp.
>>> 
>>> 
>>> 
>>> Router A is advertising 5 routes to router B, when the session 1st
>>> comes up, router B has 5 routes received from router A. After 1:15
>>> min the learned routes on router B disappear. 
>>> 
>>> 
> How are the routes getting into BGP?  Are the coming in via tie-down
> routes in the IGP somewhere?  Could it be that you have an IGP
> failure of some sort such that the routes are being withdrawn
> legitimately?   
> 
> Regards,
> 
> Mike
> 
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