ANS-C01 Question #219: Real Exam Question with Answer & Explanation

Question

A network engineer configures a second AWS Direct Connect connection to an existing network. The network engineer runs a test in the AWS Direct Connect Resiliency Toolkit on the connections. The test produces a failure. During the failover event, the network engineer observes a 90-second interruption before traffic shifts to the failover connection. Which solution will reduce the time for failover?

Options

• ADecrease the BGP hello timer to 5 seconds.
• BAdd a VPN connection to the connectivity solution. Implement fast failover.
• CConfigure Bidirectional Forwarding Detection (BFD) on the on-premises router.
• DDecrease the BGP hold-down timer to 5 seconds.

Explanation

A Direct Connect failover test shows a long interruption time (90 seconds), and the goal is to reduce this failover duration.

Common mistakes.

• A. Decreasing the BGP hello timer to 5 seconds would shorten the interval at which hello messages are sent, but BGP's detection of a dead peer primarily relies on the hold-down timer. BFD provides much faster detection than even aggressive BGP timers.
• B. Adding a VPN connection is a different connectivity solution altogether and implementing "fast failover" via VPN doesn't directly address reducing failover time for the Direct Connect connection specifically.
• D. Decreasing the BGP hold-down timer to 5 seconds would accelerate BGP's detection of a dead peer, but BFD can detect failures in milliseconds, making it significantly faster and more effective for rapid failover than tuning BGP timers alone.

Concept tested. Direct Connect fast failover with BFD

Reference. https://docs.aws.amazon.com/directconnect/latest/UserGuide/resilience-toolkit.html

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