300-420 Question 32
Select 3A network engineer is tasked with implementing route filtering on an OSPF-enabled router in the corporate network. The requirement is to prevent a specific route (10.10.10.0/24) from being advertised to one of the neighboring routers. Which of the following methods can be used to achieve this?
- A
Apply a distribute-list with an access control list (ACL) on the OSPF process.
- B
Use a prefix list in conjunction with a route-map to filter the route.
- C
Apply an inbound distribute-list on the neighbor router to block the route.
- D
Modify the OSPF area configuration to suppress the route.
- E
Use a route-map for filtering during OSPF redistribution.
Show answer and explanation
Correct answers: A, B, E
Explanation
Basic route filtering in OSPF can be accomplished using distribute-lists (with ACLs), prefix lists, or route-maps during redistribution. These methods allow administrators to selectively control which routes are advertised to neighbors. In contrast, inbound filtering on neighbors or modifying the OSPF area configuration are not valid approaches for filtering specific routes in OSPF.
- A. Correct.
Correct: Distribute-lists with ACLs can be used in OSPF to filter routes from being advertised to specific neighbors.
- B. Correct.
Correct: Prefix lists combined with route-maps are a valid method to filter routes in OSPF.
- C. Incorrect.
Incorrect: Distribute-lists cannot be applied inbound to neighbors in OSPF. Route filtering is applied on the advertising router.
- D. Incorrect.
Incorrect: Modifying the OSPF area configuration does not allow for filtering specific routes. Area configurations handle summarization and other OSPF-specific behaviors but not specific route filtering.
- E. Correct.
Correct: Route-maps can be used during route redistribution to filter specific routes in OSPF.