I have come accross an interesting affect of iBGP router reflection within a single AS. We have a number of multilayer switches accross a number of different PoPs. All running iBGP sessions back to our Route Reflectors in the Core. All routers in our network are configured for iBGP multi-path 2.
We have a customer which is dual connected within one of our PoPs. They have two routers, each connected to different access switches. The routers are assigned a /30 for their outside interface, to connect to us, and we then have static routes pointing a /27 customer allocation to each /30. Each access switch redistributes these statics into iBGP.
SW1 -> Router 1 next-hop for /27
SW2 -> Router 2 hext-hop for /27
When logged onto either of the Router Reflectors I can see both routes for the /27 in the BGP table and the routing table. The route reflector has installed bother customer routers as the next-hop address for the /27 and is load-sharing to them both.
RR1 -> /27 via SW1 and SW2
We recently had customer B, who connects at a different PoP, start talking to customer A. I have notices that the routers in other PoPs only have one router to customer A's /27. I have checked the BGP table and only recieve one route from the Route Reflectors.
SW3 -> /27 via SW1
Reading the details on RR I can see that this is stated as standard behaviour:
- Routes received from a route-reflector client and selected as best routes are propagated to all BGP peers (internal and external).
I want to know if there is some IOS knob I can tweak to get the RR to advertise both BGP paths to this /27?