350-401 Question 480
Single answerA network engineer is troubleshooting a BGP deployment in which some prefixes are not following the expected path preference. The following attributes are configured for two different BGP paths to the same prefix:
Path 1: Local Preference = 200, AS Path Length = 3, MED = 50 Path 2: Local Preference = 150, AS Path Length = 2, MED = 30
Which path will BGP select as the best path, and why?
- A
Path 1, because it has the highest Local Preference.
- B
Path 2, because it has the shortest AS Path Length.
- C
Path 1, because it has the lowest MED value.
- D
Path 2, because MED is compared before Local Preference in the BGP decision process.
Show answer and explanation
Correct answer: A
Explanation
In BGP, the attributes used to determine the best path are evaluated in a specific order. Local Preference is the first attribute considered, and Path 1 has the highest Local Preference value (200). Therefore, Path 1 is selected as the best path, even though Path 2 has a shorter AS Path Length and a lower MED value, because these attributes are evaluated later in the decision process.
- A. Correct.
Correct. Local Preference is the first attribute considered when determining BGP path preference, and Path 1 has the highest Local Preference value of 200.
- B. Incorrect.
Incorrect. While AS Path Length is a valid attribute in the BGP decision process, it is evaluated after Local Preference. Path 1's higher Local Preference makes it the preferred path despite Path 2 having a shorter AS Path Length.
- C. Incorrect.
Incorrect. MED is not compared until after Local Preference and AS Path Length, so it does not impact the decision in this scenario.
- D. Incorrect.
Incorrect. This statement is false. Local Preference is considered before MED in the BGP decision process, so Path 1 is selected.