OSPF Prefix Suppression

[lagapidis (Lazarus Agapidis)]

Hello Ruwan

@ruwanrsh

Can explain a bit about how the how ospf detect transit links when performing ospf prefix suppression .

There are two types of LSAs that we have to deal with in this lesson: The Router LSA, that is a type 1 LSA that contains prefix information about the 192.168.30.0/24 network, and the Network LSA< that is a type 2 LSA that contains prefix information about the 192.168.123.0/24 subnet.

If you notice, in each of the LSAs described, the only networks that have a prefix other than /32 are the transit networks, so if you suppress prefixes, the transit networks will be removed.

@ruwanrsh

Also, you are mentioning that /32 link is considered an invalid link in the lsdb.In such case why aren’ t the Loopback networks considered invalid when prefix suppression is enabled?

A subnet mask of /32 on a multi-access network is not possible because then it would not be a multi-access network. So if an OSPF router sees this, it knows that prefix suppression has been applied. It is not invalid in the sense that it cannot exist in the database.

I hope this has been helpful!

Laz