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Lets say we want to stop advertising an external route out of the area. We can do this with ABR External prefix filtering. This is done on the Type7-to-Type5 Translator ABR, which is the router with the highest router-id in the nssa.

This can easily be accomplished by creating a summary address on the ABR for the prefix you dont want external to the area and then specifying not-advertise as follows.

router ospf 1
 summary-address 200.0.0.0 255.255.255.0 not-advertise

The further routers will continue to have the other external routes, but not the one filtered. You will also notice that this also filters the LSA itself from being installed into the database.

 R5#sh ip ro 200.0.0.0
% Network not in table
R5#sh ip ro 200.0.1.0
Routing entry for 200.0.1.0/24
  Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric 66
  Last update from 155.1.0.3 on Serial0/0/0, 00:03:53 ago
  Routing Descriptor Blocks:
  * 155.1.0.3, from 150.1.3.3, 00:03:53 ago, via Serial0/0/0
      Route metric is 20, traffic share count is 1

R5#sh ip ospf data external 200.0.0.0

            OSPF Router with ID (150.1.5.5) (Process ID 1)

                Type-5 AS External Link States
R5#