350-401 Question 354
Select 3A network engineer is troubleshooting routing issues in an OSPF-based network. Upon inspection, it is observed that a routing loop is occurring between two routers, R1 and R2. The engineer notices that route tagging is not implemented, and split horizon is not applicable in the current configuration. Which of the following mechanisms can be used to prevent this routing loop?
- A
Enable route poisoning to mark the route as unreachable.
- B
Implement a route map with filtering on the affected routers.
- C
Enable split horizon on all interfaces in the network.
- D
Configure a higher administrative distance for the problematic route.
- E
Use route tagging to block the re-advertisement of the route.
Show answer and explanation
Correct answers: A, B, E
Explanation
Routing loops can be prevented using several mechanisms. In this scenario, route poisoning marks the problematic route as unreachable, effectively stopping the loop. Applying a route map with filtering ensures the affected route is not advertised further. Route tagging provides a method to identify and block re-advertisements, preventing loops. Split horizon is not applicable, as stated in the question, and changing administrative distance does not directly solve loop prevention.
- A. Correct.
Route poisoning is used to mark a route as unreachable by setting the metric to an infinite value, which can help break the routing loop.
- B. Correct.
A route map with filtering can be applied to block the advertisement or acceptance of specific routes, effectively preventing loops.
- C. Incorrect.
Split horizon prevents a route learned on an interface from being advertised back out of the same interface. However, the question specifies that split horizon is not applicable in this scenario.
- D. Incorrect.
Changing the administrative distance can influence route selection but does not directly address the prevention of routing loops.
- E. Correct.
Route tagging allows routers to identify and block the re-advertisement of previously advertised routes, which is a reliable mechanism to avoid loops.