Pass the Cisco CCDE v3.0 400-007 Questions and answers with ExamsMirror

In DMVPN designs with many spokes, spokes may fail to receive periodic keepalives or routing updates if queues overflow during congestion, causing holding timers to expire and tunnels to flap. Increasing the hold queue size on the tunnel interface of the spoke routers allows them to buffer control plane packets during congestion and avoid premature tunnel teardown.

Why other options are incorrect:

A, C, E: Physical interface queues do not directly affect tunnel protocol timers.

D: QoS may help prioritize control plane traffic but doesn't address queue depth directly, which is the root cause of the issue.

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The priority queue (strict priority queue) is intended for real-time, delay-sensitive traffic like voice and certain video, which have:

D. Intolerance to jitter: Real-time traffic requires consistent latency.

E. TCP-based application: Many real-time video streams and some financial trading apps use TCP but still require minimal jitter and latency.

CCDE v3.1 emphasizes that strict priority queue should only be used for traffic highly sensitive to delay and jitter to avoid starving other queues.

Why other options are incorrect:

A: HTTP-like small transactions are delay-tolerant.

B: WRED (Weighted Random Early Detection) is used for congestion avoidance, not prioritization.

C: Priority queue is specifically for traffic intolerant to loss and jitter.

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IPFIX probes can perform deep flow inspection beyond what routers/switches natively collect, making them well suited for security monitoring (DDoS detection, anomaly detection, intrusion attempts).

Probes can extract Layer 7 information unavailable from normal router flow records.

Why other options are incorrect:

A, C, D: Can also be done using router-integrated flow exports; dedicated probes are primarily deployed for advanced security visibility.

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In IoT environments, especially in manufacturing plants, security is the primary concern during migration:

IoT devices often have limited security capabilities and may introduce vulnerabilities if not properly segmented, authenticated, and monitored.

Manufacturing plants operate critical systems where availability, safety, and integrity are paramount.

CCDE v3.1 emphasizes securing data, devices, and control systems as a top priority during IoT migrations.

Other options explained:

A: Sensors are part of the IoT solution but not the primary migration concern.

C: Applications are important but typically come after securing connectivity and endpoints.

D/E: Infrastructure elements are secondary to security in the migration assessment.

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C (Transparent firewall): Operates at Layer 2, allowing filtering and inspection of traffic within the same subnet without requiring IP routing changes. It performs deep packet inspection while maintaining Layer 2 adjacency, making it ideal for intra-subnet traffic control in data centers.

This allows security segmentation inside broadcast domains, enforcing security policies even for east-west traffic.

Other options explained:

A: Routed firewalls require subnet boundaries and are not ideal for intra-subnet control.

B: VLAN ACLs provide basic filtering but lack deep packet inspection capabilities.

D: Zone-based firewalls are primarily designed for inter-subnet (Layer 3) traffic segmentation.

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: On most hardware platforms, control plane protection is implemented in hardware to safeguard CPU resources from overload due to excessive control traffic.

E: Control plane policing must be carefully sized to allow sufficient protocol traffic (OSPF, BGP, etc.) during normal and convergence periods to ensure stability.

Why other options are incorrect:

B: Policing should be applied universally, not just on external interfaces.

C: False alarms are operational issues but not design considerations.

D: Control plane policers are applied after forwarding decisions for traffic destined to the router CPU.

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Unicast Reverse Path Forwarding (uRPF)is a security feature that helps mitigate IP spoofing attacks. It checks whether the source of a packet received on an interface matches the best return path to that source in the routing table.

Strict Mode (C):Ensures the source IP address of a packet is reachable via the same interface on which the packet was received. This prevents forged source IP addresses from traversing the network, which is essential in defending against outbound DDoS attacks sourced from infected hosts.

Loose Mode (B):Only verifies that the source IP exists in the routing table (less strict), which might still allow spoofing in multi-homed or asymmetric environments.

uRPF strict mode is the best fit in secure environments with symmetric routing—commonly in enterprise edge or distribution layers.

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When an ACL is applied inbound on the Internet gateway interface facing the internal (trusted) network, the source IP address seen in the ACL will be the address after NAT translation has been applied to outbound traffic. This is called the inside global address:

Inside global = Public IP assigned by NAT to inside traffic for external use.

Inside local = Internal IP address prior to NAT.

Why other options are incorrect:

B, D: Outside addresses refer to external devices, not internal traffic.

C: Inside local is seen before NAT, not after.

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A (Additional MPLS provider):True path diversity includes provider diversity to eliminate the possibility of shared failures within a single provider’s infrastructure. Multiple providers minimize correlated failures, increasing WAN availability.

Other options explained:

B: Out-of-band management improves operational access but doesn't address WAN availability.

C: Dual-homing branches is valuable but not directly related to the data center’s WAN failure condition.

D: Hardware redundancy improves local device availability but doesn't mitigate WAN failures.

OSPF throttling timers control the pacing and frequency of SPF calculations and LSA generation. They help strike a balance between fast convergence and control-plane stability. The key timers include:

LSA generation throttling (min/max interval between LSA originations)

SPF calculation throttling (delays between consecutive SPF runs)

By tuning these timers, network designers can:

Prevent CPU overload caused by rapid or repeated LSA updates due to flapping links

Smooth out instability while still enabling responsive convergence

This approach aligns with CCDE v3.1 under “Protocol Design Implications” for optimizing IGP behavior in large, dynamic topologies.

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A (Device resiliency):Hardware redundancy (dual power supplies, supervisor modules, etc.) ensures device uptime.

D (Network resiliency):Redundant links, fast failover mechanisms, and loop-free designs ensure the overall network remains operational during failures.

Other options explained:

B: Device type is secondary if resiliency features are built-in.

C: Network type is not directly related to resiliency.

E: Network size influences scale, not availability.

Security design must be aligned with:

Business objectives (A): Security design must meet business needs without hindering operations.

Security policies and standards (B): Compliance with internal and external regulations is mandatory.

CCDE v3.1 teaches that security design always starts from business intent and policy compliance, not purely technical or scope-based factors.

Why other options are incorrect:

C & D: Security design applies to all environments, not just multi-site or new deployments.

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