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

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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C (Layer 2 switches unaffected):IPv6 operates at Layer 3, so pure Layer 2 switches forward frames without needing IPv6 awareness. As long as switches can transparently forward Ethernet frames, IPv6 functionality will be preserved, minimizing unnecessary hardware upgrades.

Other options explained:

A/B/D: These unnecessarily increase cost and complexity for basic Layer 2 functionality where IPv6 awareness is not mandatory.

When both networks use overlapping private IP addresses, a single Cisco IOS NAT router can handle bidirectional NAT with dynamic NAT (overload). However, it requires careful configuration using:

Two distinct NAT pools: One for traffic sourced from side A, and one for traffic sourced from side B.

ip nat inside source and ip nat outside source commands with the overload keyword.

Interfaces must be properly defined with ip nat inside and ip nat outside to reflect traffic directionality.

Option D is correct because it explicitly reflects the requirement to use two different NAT pools for overload in both directions, which ensures proper address translation and session tracking.

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