Multiple iBGP sessions to same router w/route-reflectors

jcartier · ‎09-09-2008

I'm in a scenario where I have two routers, configured with two loopbacks, connected together via two links. I'm in the process of transitioning from one loopback to the other and I was wondering if there are any caveats to having two sessions up...one BGP session to the first lookback (existing), then another BGP session up to the second loopback (new)...also, each router is a route-reflector client to another router upstream. Think of a triangle with the two bottom routers being route-reflector clients to the router at the top.

Giuseppe Larosa · ‎09-09-2008

Hello Jeff,

the Originator ID attribute and the cluster list attribute help to deal with this scenario:

the first is added by the route reflector and contains the BGP router-id of the advertisement originator that is only one ip address for each router so this helps a router to avoid to accept on session with loop1 the advertisement reflected back on session using loop2.

the cluster list contains: or the cluster-id if it is defined or the BGP router-id of the RR(s) that has reflected the advertisement.

It is the history of reflections.

These attributes allow to relax the iBGP rule when using RRs.

In your case the first attribute Originator ID is enough to avoid that a router re-import its own advertisements on the second iBGP session and viceversa.

These attributes are automatically generated when using Route Reflectors no explicit config is needed.

Hope to help

Giuseppe