We are multihoming using two 7600 routers, each to a separate ISP. The two 7600's then have an iBGP peering between them. I am preferring routes to the first ISP using local preference so if I do a "show ip bgp summary" I see the following (essentially) on each router:
x.x.x.x (Primary ISP Peering) Received routes 300000
y.y.y.z (Router 2) Recieved routes 100 (routes directly to Backup ISP)
z.z.z.z (Secondary ISP Peering) Received routes 300000
y.y.y.x (Router 1) Recieved routes 299900
The issue is, that if I have an issue with the Primary ISP (either the BGP session drops or I lose a lot of upstream routes), the routes shared in the peering between the 2 routers do not change. So even though most or all of the 300000 routes to the Primary ISP are lost, those changes are not getting passed on to Router 2. Thus, Router 1 has only 100 known routes to the internet, and Router 2 has 299900 routes to nowhere!
I can get things working again by clearing the session between the 2 routers, but I have to do this manually.
Question then: Why is this not happening automatically, and is there configuration I can change that will make it so?
Please let me know if more information is needed. I just don't see what I'm missing.