CCNP Is configuring OSPF in a multi-area design Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Configure area 0 as a stub area.

  Why it's wrong here

  Configuring area 0 as a stub area is invalid because the OSPF backbone must be able to carry all LSA types, including type 5 external LSAs, to ensure inter-area and external routing capability. Stub areas deliberately block type 5 LSAs (and, in totally stubby areas, type 3 LSAs as well), but the backbone cannot impose such restrictions because it must remain fully transit-capable for all traffic. Attempting this would break OSPF adjacency and inter-area reachability, so it cannot reduce LSDB size in a standardized way.

• ✓

  Configure the ABR with an area filter-list to filter type 3 LSAs.

  Why this is correct

  The area filter-list command on an ABR filters type 3 summary LSAs entering or leaving an area, directly and proactively reducing the number of LSAs in area 0's link-state database. Only type 3 LSAs that describe inter-area prefixes are affected, so selected routes are omitted from the ABR's summary advertisements without disrupting the backbone's transit role or intra-area operations. This is the only option that reduces LSDB size while maintaining correct OSPF design.

• ✗

  Configure OSPF database overflow protection.

  Why it's wrong here

  OSPF database overflow protection, configured with the 'max-lsa' command, only sets a ceiling for the total number of LSAs that a router will accept; it does not filter or suppress the initial flooding of LSAs. When the LSA count exceeds the configured limit, the router enters an overflow state and ceases OSPF operation on the interface, causing temporary outages rather than reducing the LSDB proactively. It is a safety mechanism against database overload, not a method to control inter-area route distribution.

• ✗

  Configure the ABR as an ASBR.

  Why it's wrong here

  Configuring the ABR as an ASBR would introduce external route redistribution, which generates type 5 AS-external LSAs (and type 4 ASBR-summary LSAs) that are flooded into area 0, thereby increasing LSDB size. An ABR that is also an ASBR injects additional route information rather than filtering it, so this action directly contradicts the goal of reducing OSPF overhead. This option would worsen the problem, not mitigate it.