300-410 Question 144
Single answerAn enterprise network uses BGP for interconnecting with multiple ISPs. The network administrator notices that a specific route is being learned from two different ISPs, but the traffic is preferring ISP1's path over ISP2's. Upon investigation, the administrator finds that the AS path length is the same for both routes. Which BGP path attribute is most likely causing the preference for ISP1's route?
- A
Local Preference
- B
MED (Multi-Exit Discriminator)
- C
Origin Type
- D
Next Hop
Show answer and explanation
Correct answer: A
Explanation
In BGP best-path selection, the Local Preference attribute is evaluated early in the process and is used to indicate the preferred exit point for outbound traffic from an AS. Since the AS path length is the same for both routes, the most likely reason ISP1's route is preferred is due to a higher Local Preference value being assigned to it.
- A. Correct.
Local Preference is used within an AS to prefer one route over another. It is the most likely attribute causing the preference for ISP1 since it is evaluated before other attributes like MED or Origin Type in the BGP best-path selection process.
- B. Incorrect.
MED is used to influence incoming traffic between different autonomous systems. While it can impact path selection, it is evaluated after Local Preference in the BGP decision process.
- C. Incorrect.
Origin Type is a BGP attribute that indicates how a route was introduced into BGP. However, it is considered later in the BGP decision process, making it less likely to influence the current preference.
- D. Incorrect.
Next Hop indicates the address of the next router in the path. While it is important for reachability, it does not directly influence path preference in this scenario.