400-007 Reviews Questions

B (OTV — Overlay Transport Virtualization): Allows Layer 2 extension across data centers while maintaining fault isolation by not extending STP across the WAN. Control plane handles MAC learning, which provides stability and loop avoidance between data centers.

Why other options are incorrect:

A: FabricPath is mainly for intra-data center Layer 2 fabric.

C: Advanced VPLS extends Layer 2 but carries STP across the WAN.

D: LISP operates at Layer 3, not for Layer 2 extension.

E: TRILL also focuses on intra-DC Layer 2 but not DCI fault isolation.

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STP Bridge Assuranceis a mechanism used to protect againstunidirectional link failureson point-to-point STP connections in environments likeRapid PVST+ and MST. When Bridge Assurance is enabled, BPDUs are expected on all BPDUs-capable interfaces. If a switch stops receiving BPDUs on a point-to-point link where Bridge Assurance is enabled, it assumes the link has failed and transitions the port to blocking to prevent a loop.

This is especially useful in high-availability enterprise designs that require protection from unexpected switch behavior or partial link failures.

Why other options are incorrect:

A. BPDU Guard: Protects access ports by placing them in an err-disabled state if BPDUs are received—useful at the edge, not for core loop protection.

C. MSTP: Refers to the protocol itself but does not solve the unidirectional link issue on its own.

D. TRILL: A different architecture (layer 2 routing) and not applicable to Rapid PVST+ or MST-specific protection.

SD-WAN design principles:

C: Centralized policy, simplified management, and dynamic path selection improve operational efficiency, directly resulting in cost savings.

D: SD-WAN provides centralized orchestration, automation, and zero-touch provisioning, simplifying deployment and scaling.

Why other options are incorrect:

A: SD-WAN improves performance with features like dynamic path selection but cannot inherently prevent slow underlay performance.

B: Many SD-WAN solutions logically separate control and data planes, but not all strictly follow full separation like traditional SDN.

E: SD-WAN is typically hardware-agnostic but does not depend on specialized switching hardware.