300-440 Question 136
Select 3A network engineer is configuring BGP between two routers in different autonomous systems. The routers are separated by multiple hops. To establish the neighbor relationship, the engineer has also enabled authentication for the BGP session. However, the BGP session fails to establish. Which of the following steps should the engineer take to troubleshoot and resolve the issue?
- A
Verify that the authentication passwords configured on both routers match.
- B
Ensure that the 'ebgp-multihop' command is configured on both routers with the appropriate hop count.
- C
Check that the private AS numbers are removed from the AS_PATH using the 'remove-private-AS' command.
- D
Enable the 'next-hop-self' command on both routers to ensure proper next-hop reachability.
- E
Verify that the BGP session states are progressing through the proper sequence (Idle, Connect, Active, OpenSent, OpenConfirm, Established).
Show answer and explanation
Correct answers: A, B, E
Explanation
To troubleshoot and resolve the issue, the engineer must first verify that the authentication passwords match on both routers, as mismatched passwords will prevent the session from establishing. Additionally, the 'ebgp-multihop' command is required when routers are separated by multiple hops. Finally, verifying the BGP session states helps identify where the session is failing in the establishment process. Steps like 'remove-private-AS' and 'next-hop-self' are unrelated to the neighbor relationship establishment and are therefore not correct answers.
- A. Correct.
Authentication is crucial for establishing a BGP session. If the passwords do not match, the BGP session will fail to establish.
- B. Correct.
Since the routers are separated by multiple hops, the 'ebgp-multihop' command must be configured with an appropriate hop count to allow BGP to establish a connection over multiple hops.
- C. Incorrect.
The 'remove-private-AS' command is used to remove private AS numbers from the AS_PATH before advertising routes to external peers. It does not directly impact the establishment of a BGP session.
- D. Incorrect.
The 'next-hop-self' command is used to modify the next-hop attribute for route advertisements but does not affect the BGP neighbor establishment process.
- E. Correct.
Verifying the BGP session states is essential for troubleshooting BGP connectivity issues. If the session is stuck in states like Idle or Active, it indicates a problem with the configuration or connectivity.