Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am having a difficult time figuring out one of the fundamental rules of iBGP, eBGP, and confederations.

Consider the following routers which are all in the same Autonomous System (AS)

r1 == r2 == r3

r1 is in sub-AS(confederation) 65100

r2 and r3 are in sub-AS(confederation) 65200

I know that iBGP speakers will not advertise routes learned from iBGP to other iBGP peers.

My understanding of confederations is that sub-AS's behave like eBGP peers. Perhaps this is wrong.

My question is if r2 learns of a route from r3 via iBGP will r2 advertise that route to r1? (currently this is not happening)

I know I could work around by making r1 a route reflector client of r2. I also know there are commands to disable filtering out routes that you don't actually have, but that doesn't seem right either.

I could also set static routes and redistribute them into eBGP, but I'm trying to make this scalable so I don't have to add 100s of static routes.

Is there some setting that could "redistribute" iBGP learned routes into eBGP (then I can filter which ones with a route-map)? or a setting to inject iBGP routes into eBGP?


I turned off syncronization on all routers

When I remove static routes on r2 for r3 and clear BGP sessions, r1 receives the routes for r3.

share|improve this question

migrated from Sep 4 '12 at 22:24

This question came from our site for professional and enthusiast programmers.

Have you got an IGP correctly configured here also? You said "My question is if r2 learns of a route from r3 via iBGP will r2 advertise that route to r1? (currently this is not happening)" - No, why would r2 learn a route from r3 if via iBGP, iBGP neighbours don't do that, you said this your self. r2 and r3 should have all the same internal routes learnt via the IGP, if they are in the same AS and functional iBGP neighbours. Is this how your set up is? – jwbensley Sep 5 '12 at 21:04
continuing on...r2 should only learn routes from r3 over iBGP that r3 has learnt from a neighbour (such as r4, not in your diagram, to the right of r3), that is an eBGP neighbour. – jwbensley Sep 5 '12 at 21:07

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.