Cisco CCDE 400-007 New Questions

A (Focus on the solution instead of the problem): While resolving issues quickly is important for operations, solution-oriented thinking during the design phase may overlook essential requirements analysis. Design decisions must be based on problem understanding, traffic analysis, and actual network behavior.

Other options explained:

B, C, D: All directly impact WAN design by influencing QoS, capacity planning, flow optimization, and visibility.

When multiple virtualized network zones (such as VRFs, virtual firewalls, or logical partitions) are consolidated onto a single physical device, the primary concern is:

A (Fate sharing): A single hardware failure, software crash, or resource exhaustion event could simultaneously impact all virtualized zones, creating a shared risk across multiple otherwise isolated services.

Other options explained:

B: CPU resource allocation can be controlled via resource management but is not the primary risk.

C: Congestion control is typically a traffic engineering issue, not a virtualization risk.

D: Security isolation can be maintained through proper virtualization boundaries.

E: Bandwidth can be managed through QoS and resource allocation.

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In IPv6, routers advertise prefixes via Router Advertisement (RA) messages. An attacker could inject rogue RAs to manipulate the IPv6 configuration of endpoints.

Router Advertisement Guard (RA Guard) blocks unauthorized RA messages from being received on access ports, preventing endpoints from receiving incorrect IPv6 prefixes from malicious or misconfigured devices.

This security feature is crucial when devices have IPv6 enabled but the network is IPv4-only.

Other options explained:

A: Source Guard and Prefix Guard enforce valid address and prefix assignment but do not prevent RA spoofing directly.

C: Prefix Guard focuses on controlling prefixes being assigned, not blocking RA messages.

D: Secure Neighbor Discovery (SEND) provides cryptographic protection but is rarely deployed due to complexity.

Virtual Private LAN Service (VPLS) provides Layer 2 VPN connectivity over MPLS. Each Provider Edge (PE) device must learn and maintain MAC addresses per virtual instance.

PE Scalability is the primary concern: With 2000 VLANs, each PE participating in those instances must maintain a large forwarding table and handle associated control-plane activity.

MAC learning and aging, along with full-mesh label-switched paths (LSPs), place a heavy burden on CPU and memory.

Flooding (A) is expected but not the primary concern; it’s a symptom of scale.

The underlying transport (C) and VLAN ID limits (D) are important but not as critical in the context of PE resource scalability.

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