300-420 Question 42
Single answerAn enterprise network consists of two WAN links connecting a branch office to the headquarters. The network is configured with equal-cost multi-path (ECMP) routing to enable load sharing across the two links. However, the branch office experiences uneven traffic distribution, where one link is overloaded while the other remains underutilized. What could be the cause of this issue?
- A
The hash algorithm used for load sharing is not distributing flows evenly.
- B
The link with higher bandwidth is being prioritized by ECMP.
- C
One of the links has a higher administrative distance than the other.
- D
The routing protocol used does not support load sharing.
Show answer and explanation
Correct answer: A
Explanation
Load sharing in ECMP relies on a hash algorithm to distribute flows across multiple paths. Uneven traffic distribution often occurs when the hash algorithm produces an imbalanced distribution of traffic, leading to one path being overloaded while others remain underutilized. Adjusting the hash algorithm or considering per-packet load balancing (if supported) can address this issue.
- A. Correct.
The hash algorithm determines how traffic is distributed across equal-cost paths. If the hash algorithm results in uneven distribution of traffic flows, one link may become overloaded while the other remains underutilized.
- B. Incorrect.
ECMP does not prioritize links based on bandwidth. It simply distributes traffic across paths with equal costs, regardless of their bandwidth capabilities.
- C. Incorrect.
For ECMP to work, all paths must have the same cost. Administrative distance is used to select the best route when multiple routing protocols are involved, but it is not relevant in this scenario.
- D. Incorrect.
The scenario explicitly states that ECMP is being used, which inherently supports load sharing. This option is therefore incorrect.