[c-nsp] learned routes disappear

[Paul A]

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  Could it be that you have an IGP failure of some sort such that the routes are being withdrawn legitimately?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