OSPF Intra Area Route Filtering

[Don Maker]

We have an odd situation at work where we would like to restrict an ospf neighbor in one area to only to be able to advertise a certain route. It's for an anycast scenario where an ospf process on a linux machine (not owned by the network team) needs to advertise a /32 for an anycast service. We've agreed (right now anyway) that they can advertise this into ospf using Quagga. We would like to limit the routes they can advertise to a single /25.  I can't think of any way to do this other than using a different IGP, probably iBGP to connect the Quagga process and then filtering the external routes. 

I thought about

distribute lists

but that will only prevent unwanted routes from getting into the local routing table, not the LSD. The LSAs will still flood and any downstream ospf router is going to install the routes unless the same

distribute list

is used everywhere up to the ABR where an area

filter-list

can be used to prevent the routes going to area 0. This is not a great solution and if any new routers are brought online without the

distribute list

then there will be problems. Added to which, some of these routers involved are HP procurves that I don't think can do

distribute-lists

anyway.

Does anyone have any other thoughts on something like this?

Thanks!

[Don Maker]

I think I should be able to do this with a tracked object. That way the server does not need to run a routing protocol at all. I'll have them create a loopback on the server and tell whatever service they want this for (probably DNS) to listen on the loopback address and then the connected server will create a route that tracks that server and then distribute that static route via ospf. 

This should work...

[Don Maker]

I think this should work, just not sure on the track syntax to use...

Any helpful suggestions?

[Don Maker]

I think I got it now. I created an

ip sla using icmp

and then a track object using that sla. Then a static route that uses the track. This seemed to do the trick. 

[Richard Burts · Accepted solution]

That seems to be a reasonable solution. I am glad that you have been able to find the solution to your own question. Thank you for sharing it with the forum.

HTH

Rick