300-410 Question 127
Select 3You are troubleshooting a BGP issue in a network where a router configured for VRF-Lite is not advertising routes to one of its external BGP peers. Upon investigation, you find that the BGP session is established, but no prefixes are being advertised. Which of the following could be causing this issue?
- A
The route-target export configuration for the VRF is missing.
- B
The BGP neighbor is configured with the wrong remote AS.
- C
The routes are not being imported into the VRF routing table.
- D
The 'network' statement for the prefixes is missing in the BGP configuration.
- E
The BGP session is using an incorrect source interface.
Show answer and explanation
Correct answers: A, C, D
Explanation
In VRF-Lite configurations, routes must be properly imported into the VRF routing table and associated with the correct route-target export configuration to be advertised to external BGP peers. Additionally, the 'network' statement in the BGP configuration is required to explicitly advertise the prefixes. The session being established rules out issues like incorrect remote AS or source interface configuration. Proper troubleshooting involves verifying all these parameters to ensure successful route advertisement.
- A. Correct.
The route-target export configuration is necessary for VRF routes to be advertised to external BGP peers. If missing, the routes will not be shared.
- B. Incorrect.
If the wrong remote AS is configured, the BGP session would not establish at all. Since the session is already established, this is not the cause.
- C. Correct.
Routes must be imported into the VRF routing table to be advertised. If the routes are not in the VRF table, they cannot be sent to the BGP peer.
- D. Correct.
The 'network' statement in BGP defines which prefixes should be advertised. Without it, the router will not advertise the prefixes even if they exist in the routing table.
- E. Incorrect.
An incorrect source interface would prevent the BGP session from establishing. Since the session is established, this is not the issue.