300-440 Question 143
Single answerA network engineer is troubleshooting an issue where traffic destined for a remote network is not following the desired path. The enterprise is using BGP to connect to two ISPs and has received the same prefix from both ISPs. The engineer has noticed that the traffic is going through ISP1 instead of the preferred ISP2. Which BGP attribute should the engineer modify to influence the path selection in favor of ISP2?
- A
Local Preference
- B
MED (Multi-Exit Discriminator)
- C
AS-Path Prepending
- D
Weight
Show answer and explanation
Correct answer: A
Explanation
In BGP, the Local Preference attribute is the primary mechanism to influence the path selection within an AS. It is applied to routes learned from eBGP neighbors and dictates the preferred exit point for traffic within the AS. In this scenario, modifying the Local Preference for the route received from ISP2 to a higher value than that of ISP1 will ensure that traffic destined for the remote network uses ISP2 as the preferred path.
- A. Correct.
Local Preference is the correct attribute to modify because it is used within an AS to influence the preferred exit point for traffic. A higher Local Preference value is preferred.
- B. Incorrect.
MED influences path selection between autonomous systems but is considered after Local Preference in the BGP decision process. It would not override the Local Preference value.
- C. Incorrect.
AS-Path Prepending is used to make a path less preferred by increasing the AS-path length, but it is not relevant in this scenario where Local Preference can achieve the goal more directly.
- D. Incorrect.
Weight is a Cisco-specific attribute that influences path selection only on the local router, and it is not propagated to other routers in the AS. It would not solve the issue across the enterprise network.