300-320 · Question #540
300-320 Question #540: Real Exam Question with Answer & Explanation
The correct answer is C: Use a distribution-list in the OSPF process to filter out the routes. OSPF does not natively support route filtering within an area (LSAs flood the entire area), but two valid approaches exist at the routing table or redistribution layer. A distribute-list under the OSPF process filters routes from being installed into the local routing table (RIB)
Question
Options
- AUse a different routing protocol such as EIGRP between the networks
- BConfigure a different OSPF area that would prevent any unwanted routes from entering the
- CUse a distribution-list in the OSPF process to filter out the routes
- DUse access list on the ingress interface to prevent the routes from entering the network
- EDesign a filter using prefix list to ensure that the routes are filtered out at the redistribution point
Explanation
OSPF does not natively support route filtering within an area (LSAs flood the entire area), but two valid approaches exist at the routing table or redistribution layer. A distribute-list under the OSPF process filters routes from being installed into the local routing table (RIB) without affecting the OSPF database itself-effective for inbound filtering on a specific router. A prefix-list applied at the redistribution boundary filters which routes are redistributed between the two OSPF domains (or into/out of OSPF), preventing unwanted partner routes from entering the network at the source. Using a different protocol does not solve the filtering problem. Interface ACLs block data-plane packets, not control-plane routing updates. A different OSPF area alone does not prevent routes from propagating.
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