ospf route filtering question

Unanswered Question
Jun 9th, 2007

How do I prevent OSPF routes from entering another router's OSPF database?

---Sarah

I have this problem too.
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mohammedmahmoud Sat, 06/09/2007 - 11:14

Hi Sarah,

AFAIK, you can't filter LSAs from entering OSPF database, but you can filter routes from being injected to the routing table from the OSPF database using distribute-lists for example.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

sarah12345 Sat, 06/09/2007 - 12:36

Hi Mohammed,

Thanks!

So as long as both routers use OSPF, there is no way to prevent the LSAs entering the OSPF database? The only solution is to use another routing protocol?

Sarah

mohammedmahmoud Sat, 06/09/2007 - 12:43

Hi Sarah,

You are welcomed, in brief OSPF populates the OSPF database via the LSAs, and then it calculates the SPF tree using the Dijkastra's algorithm using the database, from the tree the routes are deduced and then injected into the routing table, at this point you can filter which route to add to the routing table and which route you desire to filter, this can be simply done via a distribute list.

Why do you think that you need another routing protocol ?

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

ariela Sun, 06/10/2007 - 02:43

Hi,

no way, as correctly Mohammed says, to filter some specific LSAs, but to filter ALL outgoing LSAs to an OSPF neighbor you can use the 'neighbor database-filter all out' command in router configuration mode for point-to-multipoint networks, or 'ip ospf database-filter all out' command on an interface basis for broadcast, nbma and point-to-point networks.

This is normally used to block the LSA flooding on a large full mesh topology.

More infos:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfospf.htm#wp1001572

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfospf.htm#wp1002321

HTH

Andrea

Edison Ortiz Sun, 06/10/2007 - 12:22

You can do it by using areas. You can place the interfaces you want to filter in a different area and then you can perform LSA Type 3 filtering.

If you tell us the network configuration you are thinking of, we can come up with a solution to prevent neighbor routers from being injected.

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