400-007 Exam Dumps - Cisco Certified Design Expert (CCDE v3.1)

B (Weighted Random Early Detection - WRED):WRED proactively drops packets before buffers are full to avoid global synchronization in TCP traffic and prevent tail drops, thus improving overall TCP performance under congestion.

Other options explained:

A: WFQ provides fairness but does not proactively avoid congestion.

C: LLQ is for delay-sensitive traffic, not congestion avoidance for TCP.

D: FIFO offers no QoS or congestion control.

C (Both modes use control packets):Regardless of whether echo packets are used, BFD asynchronous mode always relies on periodic transmission of control packets to verify session liveliness.

E (Echo mode uses separate packets):When echo is enabled, the echo packets are transmitted in addition to control packets, providing even faster failure detection by relying on data plane processing.

Other options explained:

A: Control and echo packets are never combined into a single packet.

B: Both modes always use control packets; echo packets are optional.

D: BFD echo packets are locally looped, not reflected back from the remote device.

C (Class-Based Weighted Fair Queuing - CBWFQ): CBWFQ allows assigning bandwidth limits (in this case, 2 Mbps) to specific traffic classes, effectively controlling scavenger traffic without dropping excess packets unnecessarily.

Other options explained:

A: Policing drops excess traffic immediately rather than queuing.

B: LLQ is for delay-sensitive traffic, not scavenger control.

D: Shaping is useful but typically applied at interface level, not specific traffic classes.

B (Hybrid cloud): Combines private infrastructure with public cloud capabilities, offering flexibility for changing technology requirements while controlling operational expenses. The enterprise can invest CapEx in private resources while using public cloud elasticity for dynamic bandwidth or compute needs.

Hybrid solutions allow gradual migration and innovation while maintaining control and compliance over sensitive workloads.

Other options explained:

A: Private cloud limits flexibility and increases CapEx.

C: Public cloud minimizes CapEx but may increase OpEx for unpredictable workloads.

D: Multicloud adds complexity and often increases OpEx and operational management overhead.

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Policy-Based Routing (PBR) allows traffic from a specific source (172.16.2.0/24) to follow a user-defined path (via Singapore), overriding the default ECMP behavior.

This solution is optimal for traffic steering when granular control is required for specific prefixes while leaving the rest of the traffic to use default ECMP routes.

Why other options are incorrect:

B: Route summarization affects route advertisements, not traffic forwarding paths for specific prefixes.

C: Unequal-cost load balancing influences overall ECMP behavior, not source-based forwarding control.

D: Loop-Free Alternate (LFA) is for fast failover, not policy-based forwarding decisions.

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A (Design expecting outages and attacks):In WAN design, resiliency requires assuming that failures and attacks will occur. This drives the use of redundancy, diverse paths, and proactive failure mitigation techniques.

Other options explained:

B/C/D: While important, these focus on operational efficiency rather than core resiliency principles.

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.