300-420 Question 221
Single answerAn enterprise network is designed with a primary MPLS link for WAN connectivity and a secondary LTE link as backup. The LTE link should only be used during primary link failures and must automatically restore primary connectivity when the MPLS link becomes available. Which technology should be implemented to achieve this requirement?
- A
Static route with a higher administrative distance for the LTE link
- B
Equal-Cost Multi-Path (ECMP) routing across both links
- C
Bidirectional Forwarding Detection (BFD) for the LTE link
- D
Policy-Based Routing (PBR) to force traffic through the LTE link
Show answer and explanation
Correct answer: A
Explanation
To meet the requirement of automatic failover and restoration, static routes with appropriate administrative distances are the best solution. The MPLS link is configured with a lower administrative distance, making it the preferred path, while the LTE link has a higher administrative distance and acts as a backup. This ensures seamless failover when the MPLS link fails and automatic restoration when it becomes available again.
- A. Correct.
Static routes with a higher administrative distance allow the LTE link to act as a backup. When the MPLS link fails, the LTE route becomes active, and when MPLS recovers, it is automatically preferred due to its lower administrative distance.
- B. Incorrect.
ECMP is used for load balancing across multiple paths with equal costs. This does not fit the requirement, as the LTE link should only be used as a backup, not simultaneously with the MPLS link.
- C. Incorrect.
BFD is a fast failure-detection mechanism that helps in identifying link failures quickly but does not inherently manage backup connectivity or restore priorities between links.
- D. Incorrect.
PBR is used to override routing decisions based on policies. While it can route traffic through the LTE link, it does not provide an automatic failover and restoration mechanism.