This is a scenario I'm sure some of you guys have encountered.
I have two routers. Each one has a link to the telco provider. One is 10M (line1) and the other is 2M (line2). R1 is connected to line1, and R2 is connected to line2. They are backbone area routers.
The issue is the following: most of the LANs of our branches are learned through R2. But some routes are learned through R1.
I first thought it's a matter of OSPF costs. Both my routers are connected to the telco, so I thought that R2, when it computes routes to branches, finds that it's preferable to reach them through ISP PE2 (connected on line2) than through R1 (which has a better WAN bandwidth).
Telco told me to configure "filters" as they said :-), I thought of distribute lists and route-maps.