about OSPF and LSA filtering

[ariela]

Hi folks,

what the difference between 'ip ospf database-filter all out' and 'passive interface'?

Thanks for your support

Regards

Andrea

[devang_etcom]

hi Andrea,

you can have clear idea by considering the two router with the redundant link connection and runing ospf

ip ospf database-filer all out:

To prevent the flooding of link-state advertisements (LSAs) on an interface. Many Internet service providers employ redundant links between OSPF neighbors. When an OSPF router receives an LSA, the LSA is flooded on all OSPF interfaces except for the interface on which the LSA was received. The ip ospf database-filter all out command enables an ISP to choose between flooding overhead and flooding reliability. For example, if there are two links between OSPF neighbors, this command can be used to prevent the flooding of LSAs on one of the links.

Initial Cisco IOS Software Release: 12.0

this command automatically stop the flodding of LSA to the redundant link interface...

where in PASSIVE INTERFACE you have to manually configure the interface to prevent the LSA flooding...

hope this will clear your idea

rate this post if it helps

regards

Devang

[ariela]

I've another idea, maybe wrong.

passive interface = no adjacency

database-filter = adjacency, but no LSA flooding (maybe 2-way state?)

Any help will be appreciated

Regards

Andrea

[omadrid]

Ariela,

You got it on this second post.

The difference is that ospf with passive-interface there is no ospf neighbor adjacency thus no routes are learned from ospf.

With 'ip ospf database-filter all out' on the interface, it the router does form adjacency, it learns the routes propagated by ospf from its neighbors, but does not advertize anything.

It is the same thing as rip with passive-interface.