Cisco Updated 400-007 Exam Questions and Answers by stefania

Comprehensive and Detailed Explanation From Exact Extract of Design Expert (CCDE)

Summarization reduces control plane state by abstracting detailed route information. As packets move further away from the destination subnet, the network advertises summarized prefixes instead of individual host or subnet routes, minimizing control plane overhead and routing table size. This helps scale large networks and improves convergence times.

While aggregation and summarization are related, summarization specifically refers to the propagation of route prefixes and their abstraction — making it the precise fit for this question.

B (Added redundancy): Redundancy ensures alternate paths or systems are available if a failure occurs, which is the primary design principle behind resiliency. Redundancy directly contributes to higher network availability and fault tolerance.

Why other options are incorrect:

A: Load-balancing optimizes performance but doesn’t inherently improve resiliency.

C: Confidentiality addresses security, not resiliency.

D: Reliability is an outcome, not a design principle itself.

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D (Root Guard): Prevents unauthorized devices from becoming the STP root by blocking superior BPDUs on access ports.

E (BPDU Guard): Immediately shuts down ports that receive unexpected BPDUs, protecting against accidental or malicious connection of switches to access ports.

Why other options are incorrect:

A: Loop Guard protects against unidirectional link failures but not unauthorized devices.

B: PortFast speeds up STP convergence on access ports but does not provide security.

C: DTF (Dynamic Trunking Protocol) is not a security feature.

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