Cisco Updated 400-007 Exam Questions and Answers by melanie

During massive BGP update events (such as after a topology change), a route reflector may struggle processing both BGP updates and the resulting TCP acknowledgments required for reliable BGP session communication.

Increasing the hold queue size allows the router to buffer more packets waiting for processing (including TCP acknowledgments), helping the router handle bursts of BGP updates without dropping TCP segments or tearing down sessions.

This queue tuning is a well-known scalability optimization in CCDE v3.1 when designing route reflector clusters handling large-scale control plane updates.

Why other options are incorrect:

B and C: Adjusting buffer sizes does not directly address TCP acknowledgment backlog.

D: Keepalive timers control session liveliness, not update processing.

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In a standard 3-tier data center architecture (access, aggregation, core), the Layer 2-to-Layer 3 boundary typically resides at the aggregation layer. When extending VLANs between data centers using a Layer 2 interconnection, the most optimal and scalable termination point is at the aggregation layer because:

It naturally handles VLAN demarcation and Layer 3 boundary.

Spanning Tree Protocol (STP) domains remain contained within local aggregation blocks.

The core remains Layer 3-only, ensuring scalability, stability, and no STP involvement.

Simplifies traffic engineering, FHRP operations, and minimizes control-plane complexity across sites.

This design is consistent with CCDE v3.1 best practice where VLAN extension is isolated to aggregation to avoid STP scaling issues and maintain hierarchical design principles.

Why other options are incorrect:

A: STP isolation can still be achieved at aggregation while keeping the core Layer 3.

C: Access layer extensions would increase STP scope and complexity unnecessarily.

D: Core termination violates Layer 3 core design, bringing STP into the core, which is not scalable.