BGP HELP!!

myk_roque

Conditions where BGP propagate routes really confuses me I have read from Cisco Press that an iBGP router will propagate a route if the route is a directly connected route... they further state that if the update was receieved from a BGP peer within the same AS, a BGP router can propagte this route to only an eBGP peer...

What I want to know is,.. a BGP peer in the same AS is actually an iBGP peer yes? therefore,... would it be safe to say that a route learned from an iBGP peer will be propagated only to an eBGP?

wildfire

BGP Confuses the best of us so dont feel so bad! Just dont let it get you down.

A route learned by an iBGP router will not propogate a route that was learned from a peer with the Same AS number.
This route is propogated into another AS by giving it to an eBGP peer

A BGP peer in the same AS establishes an iBGP relationship.

So in answer yes you were right.

Remeber iBGP needs to be fully meshed or this information will not propogate correctly.

Read up on BGP peer groups here

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093fb7.shtml

kamal_n_m

Adding to what wildfire said, iBGP routers don't need to propagate the routes to other neighbors since we have a fully mesh neighborship, all the iBGP routers will learn the routes from the eBGP router. The iBGP routers are only supposed to learn those routes and update their routing table accordingly. They don't forward to the neighbors but use the routes for their own routing. That is the reason we say that we should have a fully mesh topology so that all the routers have the routes to go out of the AS in the correct way and through the correct eBGP router.


Regards,

Kamal

darkuser

it's not that confusing when you understand it

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfbgp.htm

myk_roque

Ive read and re-read a lot of materials on BGP... thanks for the link DK... More Information to scrounge in my brain... I think my confusion lies on the fact that I have 0 experience save for some sim configurations.

Id like to verify something though. I know that iBGP will never propagate routes to its iBGP peers. EXCEPT in the case of route reflectors and... if the route is locally generated.

My question though is, If I redistribute routes to BGP, would it qualify as a "Locally Generated route" and be propagated on to the other iBGP peers.

I do know that BGP uses keepalives to keep its connection with its peers active. So ... correct me if I am wrong, BGP needs only to propagate its route once.