[c-nsp] Preferring OSPF over BGP

[Grzegorz Janoszka]

If a router has different sources (different routing protocols) for the 
same route, it chooses the one with the smallest administrative distance:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml

The problem in short: there is a pretty big network with many routers, 
Cisco only. One of them has a network connected which it redistributes 
to OSPF. All other routers see the route via OSPF and via eBGP. Because 
of default administrative distance values, eBGP route always wins, so 
the traffic to that network from all routers but the one connected, 
always chooses external carriers, not the internal network.

One of the solutions is to change globally administrative distance for 
OSPF or BGP. However it is pretty dangerous to do it for all the routes 
on the core routers and Cisco even advices:

"a change in the administrative distance can lead to routing loops and 
black holes. So, use caution if you change the administrative distance."

I thought about setting lower administrative distance in a 
route-map/route-policy, but it seems impossible.

Right now we have filtered such prefixes from eBGP peers, but it leeds 
to total unavailability when the connected route goes down.

Do you know any solutions to prefer the route (connected on another 
router) over eBGP? The only solution that comes to my mind is to 
redistribute connected to iBGP with higher local-preference than eBGP, 
but maybe you know some better way to achieve the goal.

Thanks for any advices.

-- 
Grzegorz Janoszka