300-440 Question 135
Select 2A network engineer is troubleshooting a BGP neighbor relationship between two routers, R1 and R2. The neighbor relationship is not forming, and the 'show ip bgp neighbor' command indicates that the BGP session is stuck in the 'Idle' state. Both routers are directly connected via a Layer 3 link, and their configurations appear correct. Which of the following issues could be causing the problem?
- A
Mismatched BGP authentication configurations between R1 and R2
- B
Incorrect next-hop IP address configured on R1
- C
BGP multi-hop is not enabled on R1
- D
Private AS numbers are being used on both R1 and R2
- E
The BGP session is not synchronized with the underlying IGP
Show answer and explanation
Correct answers: A, E
Explanation
A BGP neighbor relationship stuck in the 'Idle' state typically indicates a problem with authentication or basic session establishment. In this scenario, mismatched authentication configurations (Option 1) could prevent the session from progressing. Additionally, the 'synchronization' issue (Option 5) could prevent the session from forming under certain configurations. Other options, such as multi-hop or private AS numbers, are not relevant to this direct connection scenario.
- A. Correct.
Mismatched BGP authentication configurations can prevent a BGP neighbor relationship from forming, leaving the session in the 'Idle' state. Authentication must match on both sides for a successful session.
- B. Incorrect.
The next-hop IP address is not relevant for establishing the BGP neighbor relationship in this scenario because the routers are directly connected, and the issue is related to the session state ('Idle').
- C. Incorrect.
BGP multi-hop is only required when the BGP peers are not directly connected. Since R1 and R2 are directly connected, this is not the cause of the issue.
- D. Incorrect.
The use of private AS numbers does not prevent the establishment of a BGP neighbor relationship. They are valid for private networks and are not inherently problematic in this scenario.
- E. Correct.
The lack of synchronization between BGP and the underlying IGP can cause issues with route advertisement and propagation, but it does not prevent the BGP neighbor relationship from forming.