300-420 Question 34
Single answerAn enterprise network is experiencing suboptimal routing due to multiple paths being available for certain destinations. The network engineer decides to adjust the path preference attributes to ensure that traffic flows through the primary MPLS link, with a backup link being used only in case of failure. Which attribute should the engineer configure to achieve this result?
- A
Adjust the BGP Local Preference for the primary path to a higher value
- B
Modify the IGP cost to make the backup path more preferable
- C
Configure BGP MED (Multi-Exit Discriminator) on the backup path with a lower value
- D
Use AS Path Prepending on the primary path to make it less desirable
Show answer and explanation
Correct answer: A
Explanation
To ensure the primary MPLS link is preferred for traffic, the BGP Local Preference attribute should be adjusted to a higher value for the primary path. Local Preference is one of the key attributes for determining path preference within an autonomous system, and it takes precedence over other attributes like AS Path and MED in the BGP decision-making process. The other options either do not impact BGP path selection appropriately or contradict the requirement.
- A. Correct.
Adjusting the BGP Local Preference to a higher value for the primary path ensures that it is selected over other paths within the same autonomous system. This is the correct method for preferring the primary MPLS link.
- B. Incorrect.
Modifying IGP cost will not influence BGP path selection directly. BGP path preference is determined by attributes like Local Preference, AS Path, MED, etc., not IGP cost.
- C. Incorrect.
Configuring a lower MED value would make the backup path more preferable, which contradicts the goal of prioritizing the primary MPLS link.
- D. Incorrect.
AS Path Prepending makes a path less desirable by artificially increasing the AS path length. This is not suitable for prioritizing the primary path.