[c-nsp] ebgp and ibgp

[Darryl Dunkin]

IBGP sends the best route to the other IBGP peers, not both. Border2
knows about the multiple routes itself, but only sends the one best path
to Border1.

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Shaun R.
Sent: Wednesday, October 01, 2008 16:04
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] ebgp and ibgp

Until today i had the following... Two border routers(7206VXR) connected
to 
a 3750 Stack.  the borders do ibgp with each other and the borders and 
3750's do OSPF.  Here's a quick text network design i created. 
http://unix-scripts.com/network/design.txt

Today i brang on a new provider, since most of my traffic is directed
out 
border1 and decided to add the provider to border2.  Now i'm not sure if

things are working right.  If i do a `sh ip bgp 72.14.207.99` on border1
i 
see two paths.  one path is out ProviderC on border2 and the other path
is 
out ProviderA on border1.

Now if i do the same thing on border2 i see 3 paths availible.  One out 
providerC on border2, one out providerB on border2, and other out
providerB 
on border2.  All three of these paths are out border2... what happened
to 
the paths out border1?

I'm not sure if maybe i have my ibgp configured wrong.  If i do a sh ip
bgp 
sum on border2 i see the border1 session but it only shows 71033
prefix's. 
If i do the same on border1 i see the border2 session and it shows
244993 
prefix's.

Anybody give me a idea about what may be happening here... My
understanding 
here is that if a packet comes into border1 and the better exit provider
is 
connected to border2 that border1 should send it to border2 and then out
the 
provider and vis verse.

~Shaun 


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