Redistribution of BGP into OSPF by area

[bwisner]

I need to redistribute routes from BGP into OSPF - but only in a specific area. The router doing the redistribution has several OSPF areas, including some that are NSSA. I don't want the BGP routes getting into these NSSA areas. When I look at the OSPF database, I can see the BGP routes in ALL the OSPF areas on the router. Is there a way to redistribute BGP into only certain OSPF areas? (Besides using multiple ospf processes)

Thanks

Bonnie Martin

ARINC, Annapolis MD

[thisisshanky · Accepted solution]

If the number of networks to be redistributed into the area are small....you can use the area filter-list command, and specify the prefix you are reditributing from BGP to OSPF, and the area ids of the NSSA, so that all those routes will be filtered while advertising OSPF routes to the NSSA.

This would seem to be an administrative overhead if the number of routes being advertised, is too large...

[bwisner]

Thanks for the tip. That's the kind of command I needed, but I have to upgrade my IOS to use it. I'm testing it out now.

Thanks again

Bonnie

[mark-obrien]

Bonnie,

I don't know if this is a moot point by now, or if you have already discovered this solution. I was reading something recently (Routing TCP/IP Vol. 1, by Jeff Doyle - strongly recommended to anyone who, for instance, knows what a NSSA is) and part of it reminded me of your post. When you have a router that is both an ABR and an ASBR, and some of its areas are NSSAs, you can prevent external routes from being redistributed into a NSSA with the keyword "no-redistribute" in the "area (id) nssa" command. So, change the nssa command to "area (id) nssa no-redistribute" and type 7 LSAs will not be generated for that NSSA. You may want to include the "no-summary" and/or the "default-information-originate" keywords in the NSSA statement as well, depending on your situation.

I hope this helps, and that it is not too late.

Mark

[bwisner]

Mark,

Thanks for the message, I didn't realize you could add 'no redistribute' to the area command. I'll keep that in mind for next time. For now we actually decided that running IBGP among our core routers was a better solution than redisributing OSPF. It means an extra routing process, but the 7500's should be able to handle it.

We have a lot of interfaces to other networks and redistribution is always tricky.

Thanks again!

Bonnie