Cisco 400-007 Based on Real Exam Environment

Route Distinguishers (RDs) are fundamental to MPLS Layer 3 VPN architecture (RFC 4364). They allow the service provider to distinguish identical IP prefixes from different VPN customers by adding a unique identifier to each VPN route, preventing conflicts from overlapping IP spaces.

Unique RDs ensure that the VPNv4 address family maintains separation of identical customer prefixes.

Why other options are incorrect:

B: Route Targets control route import/export policy but do not differentiate overlapping prefixes.

C: NAT is not required inside MPLS VPN for overlapping IPs.

D: VRF IDs are local identifiers on routers; not relevant for prefix uniqueness in control plane.

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A (Confidentiality): Protects information from unauthorized access.

D (Availability): Ensures resources are accessible when needed.

E (Integrity): Ensures data is not tampered with or altered improperly.

These three form the core of information security design principles known as the CIA triad (Confidentiality, Integrity, Availability), directly referenced in CCDE v3.1 security design sections.

Why other options are incorrect:

B, C, F: While important for network design, they are not part of the core security protection objectives.

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A (PPDIOO - Prepare, Plan, Design, Implement, Operate, Optimize):PPDIOO is Cisco’s structured lifecycle methodology designed specifically for network design, deployment, and management. It ensures continuous improvement, iterative design, and aligns technical efforts with business goals throughout the entire network lifecycle.

Other options explained:

B: Waterfall is a generic software development methodology.

C: Spiral emphasizes iterative risk management for software development.

D: V model applies primarily to software verification and validation.

B (MST — Multiple Spanning Tree): Bundles multiple VLANs into fewer STP instances, minimizing the scope of TCN propagation, which helps reduce MAC table flushing and unicast flooding.

Why other options are incorrect:

A: PVRSTP still processes TCNs per VLAN, increasing flooding.

C: Legacy STP behaves similarly but is not optimized for multiple VLANs.

D: PVSTP+ generates TCNs per VLAN like PVRSTP.

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