300-440 Question 122
Single answerA network engineer is tasked with configuring path preference for a branch office router that uses both BGP and OSPF to reach the same prefix (10.10.10.0/24). The goal is to ensure the BGP route is preferred over the OSPF route for this prefix. Which approach should the engineer take?
- A
Increase the OSPF cost for the branch office router to make the OSPF route less preferred.
- B
Set a lower MED value on the BGP route for the prefix.
- C
Configure a higher local preference value for the BGP route.
- D
Use route filtering to suppress the OSPF route for the prefix.
Show answer and explanation
Correct answer: C
Explanation
When deciding path preference between BGP and OSPF, BGP's lower administrative distance (20 for eBGP, 200 for iBGP) already makes it more preferred over OSPF (110). However, to explicitly ensure that the BGP route is preferred, configuring a higher local preference value on the BGP route is the correct approach. This leverages BGP's path selection attributes to influence traffic routing without disrupting OSPF functionality.
- A. Incorrect.
Increasing the OSPF cost will affect the internal OSPF path selection but will not directly prioritize BGP over OSPF. BGP and OSPF have different administrative distances, and this approach does not directly address path preference between the two protocols.
- B. Incorrect.
MED (Multi-Exit Discriminator) is used for influencing route selection between BGP peers within the same AS or between different ASes, but it does not apply to path selection between BGP and OSPF.
- C. Correct.
Configuring a higher local preference value for the BGP route is a valid method to prioritize it. Local preference is a BGP attribute used to influence outbound traffic within an AS, and it can ensure the BGP route is preferred over OSPF when combined with BGP's lower administrative distance.
- D. Incorrect.
Suppressing the OSPF route using route filtering would prevent the OSPF route from being considered, but this is not an optimal solution as it unnecessarily eliminates redundancy and flexibility in path selection.