H12-821_V1.0 · Question #922
When filter policy is used in OSPF, routing control can be achieved by filtering LSAs.
The correct answer is B. FALSE. B is correct because OSPF filter policies do not filter LSAs - they filter routes in the routing table. OSPF is a link-state protocol where LSAs must be flooded to all routers within an area to maintain a consistent topology database (LSDB); selectively dropping LSAs would…
Question
Options
- ATRUE
- BFALSE
How the community answered
(60 responses)- A27% (16)
- B73% (44)
Explanation
B is correct because OSPF filter policies do not filter LSAs - they filter routes in the routing table. OSPF is a link-state protocol where LSAs must be flooded to all routers within an area to maintain a consistent topology database (LSDB); selectively dropping LSAs would break this consistency and violate OSPF's design. Filter policies in OSPF work on the routing table level (filtering which routes get installed), not on the LSA flooding process itself.
Why A is wrong: Confusing route filtering with LSA filtering is a common misconception. You can control which routes appear in the routing table via filter policy, but the underlying LSAs are still propagated - the LSDB stays intact.
Memory tip: Think of LSAs as the "news broadcast" - every router in the area must receive the same broadcast to have the same map. Filter policies are like choosing which roads you'll drive on, not blocking the broadcast itself. OSPF = same map everywhere; filtering only affects which paths you use.
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