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OSPF database-filter

Can anybody explain where the interface configuration of ospf database-filter will be usefull in real time scenario.

Also can anyone tell me if the configured interface will continue to send hello packets as usual by blocking only ougoing LSA.Also will all other routers remove the LSA's after max age interval is reached if it is affected what are the consequences on OSPF.

Will enabling this feature affect the neighbour or interface state machines.

Please respond asap.

Thanks in anticipation.

3 REPLIES
Cisco Employee

Re: OSPF database-filter

not sure what database-filter feature you're talking about.

Until recently you could not filter the ospf database except on the ASBR.

New features were introduced to filte routes between areas.

Personally, I'm not aware of a per interface filter.

Do you have any pointer to some documentation ?

Re: OSPF database-filter

Thanks for the reply,

The concerned link is :

Block OSPF LSA Flooding

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_c/1cprt1/1cospf.htm#xtocid2712628. This was introduced in IOS 12.0.

If you can provide more information about the usefull ness of this feature it will be great.

Re: OSPF database-filter

It is something like the mesh-group concept in ISIS. Basically, this is a tuning feature that can help you prevent excessive flooding in an OSPF network. Let me give you an example. Let's say you have a bunch of OSPF routers that are point-to-multipoint full-mesh neighbors over, say, a low-speed frame-relay cloud. When a change occurs in the network, LSA's must be propogated around all routers in the same area, and so each of those frame-relay neighbors must propogate LSA's to each neighbor. So you end up with x*(x-1) LSA's going over the frame-relay links, where x is the number of frame-relay routers. In such a situation, you may not need or want so many of these LSA's going over those links, so you might use the LSA-flooding feature to prevent some (but not all) of those LSA's from being flooded. Obviously you still need some LSA's to be flooded, otherwise changes in the network will never be propogated. But you don't need all the flooding that would occur normally, and this is a way to cut down on it.

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