300-420 Question 36
Single answerYou are designing a multi-site enterprise network that uses BGP for inter-site connectivity. The customer requires that traffic destined for a specific branch location should always prefer a primary link unless it becomes unavailable. Which BGP attribute would you configure to influence the path preference for this requirement?
- A
Local Preference
- B
AS Path Prepending
- C
Multi-Exit Discriminator (MED)
- D
Weight
Show answer and explanation
Correct answer: D
Explanation
In this scenario, the Weight attribute is the best choice because it has the highest priority in the BGP decision-making process and can enforce strict path preference on a per-router basis. While other attributes like Local Preference and MED can influence routing decisions, they are not as decisive or specific to the scenario's requirements. Weight is local to the router and ensures that the primary link is always preferred for outbound traffic unless specified otherwise.
- A. Incorrect.
Local Preference is used to influence outbound traffic within an AS, but it does not directly affect path selection for incoming traffic from external peers.
- B. Incorrect.
AS Path Prepending is typically used to make a path less desirable by adding additional AS hops, but it does not enforce strict path preference for a primary link.
- C. Incorrect.
Multi-Exit Discriminator (MED) is used to influence inbound traffic path selection between multiple connections to the same AS but is not the most suitable attribute for enforcing strict primary link preference.
- D. Correct.
Weight is a Cisco-specific BGP attribute that has the highest priority in the BGP decision process. It can be used to ensure that a specific path is preferred over others for outbound traffic when configured appropriately.