300-420 Question 38
Single answerAn enterprise network is using BGP with a single route reflector (RR) to simplify its iBGP full-mesh topology. During a network audit, you discover that some routes are not being advertised to all clients of the RR. What is the most likely cause of this issue?
- A
The route reflector is not configured with the correct cluster ID.
- B
The clients of the route reflector are not configured with the 'next-hop-self' command.
- C
The route reflector is not applying outbound route policies to its clients.
- D
The route reflector clients are not configured with the 'route-reflector-client' command.
Show answer and explanation
Correct answer: D
Explanation
In a BGP route reflector setup, the RR must know which peers are its clients. This is achieved by configuring the 'route-reflector-client' command on the RR for each client. Without this configuration, the RR treats these peers as regular iBGP peers, and routes are not reflected between them, leading to incomplete route advertisements. Ensuring the correct configuration of 'route-reflector-client' resolves this issue.
- A. Incorrect.
The cluster ID identifies the route reflector's cluster and prevents routing loops. While an incorrect cluster ID can cause issues in complex topologies, it does not directly result in routes not being advertised to all clients.
- B. Incorrect.
The 'next-hop-self' command is used to modify the next-hop attribute in BGP updates but does not affect the basic route advertisement behavior of the RR.
- C. Incorrect.
Outbound route policies can filter or modify routes sent to clients; however, the lack of such policies does not explain the basic functionality of route advertisements by the route reflector.
- D. Correct.
If the clients of the route reflector are not explicitly configured with the 'route-reflector-client' command, the RR will not treat them as clients. This results in the RR not reflecting routes to and from those clients, causing the issue described.