[c-nsp] Preferring OSPF over BGP

[Martin Komon]

I believe BGP backdoor would help technically. I say technically because
in your situation it may be too demanding to implement (you mention many
routers) and may not scale well with your needs.

Take a look at BGP backdoor and decide by yourself:
> http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#bgpbackdoor

HTH,

Martin

On 8/13/2010 10:47 PM, Grzegorz Janoszka wrote:
> 
> 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.
>