300-320 Question #409: Real Exam Question with Answer & Explanation

The correct answer is C: route summarization. Route summarization is the best mechanism to insulate the broader network from the instability caused by a rapidly flapping link. When a specific subnet's link flaps, it normally triggers continuous route withdrawal and re-advertisement throughout the network, causing widespread

Question

A network link is going up and down rapidly, and it is hindering network performance and routing table stability. Which option can be configure to insulate against the performance impact of interface or link failure throughout the network?

Options

ADistributed Cisco Express Forwarding switching
BSecondary IP addressing
Croute summarization
Ddefault route propagation

Explanation

Route summarization is the best mechanism to insulate the broader network from the instability caused by a rapidly flapping link. When a specific subnet's link flaps, it normally triggers continuous route withdrawal and re-advertisement throughout the network, causing widespread SPF recalculations and routing table churn. By summarizing multiple specific routes into a single aggregate (summary) route, the summary remains stable in the routing table as long as at least one more-specific route remains reachable. The flapping of one component subnet does not force a change to the advertised summary, shielding upstream and downstream routers from the instability. Distributed CEF (A) improves forwarding performance but does not reduce routing protocol convergence events. Secondary IP addressing (B) provides redundant addresses but does not hide link instability from the routing domain. Default route propagation (D) provides a fallback path but does not suppress route churn from flapping interfaces.

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