400-007 Practice Questions

The distribution layer serves as the boundary between the access and core layers in the three-tier hierarchical design. It plays a crucial role in providing policy enforcement, control, and boundary functions, including:

QoS classification and marking (C): The distribution layer serves as the boundary for Quality of Service policies. It marks and classifies traffic as it moves from access to core layers, ensuring proper QoS treatment in the core.

Redundancy and load balancing (E): The distribution layer provides link redundancy (e.g., dual-homing access layer switches) and performs load balancing to optimize path selection toward the core.

Other options explained:

A (Fast transport): Typically associated with the core layer, which focuses on high-speed forwarding.

B (Reliability): While reliability is a network-wide goal, it’s not a primary function of the distribution layer specifically.

D (Fault isolation): While partial fault containment occurs, primary fault isolation happens at the access layer.

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A: Flow-based analysis allows understanding bandwidth usage across apps and sessions, crucial for voice/video capacity management.

C: Call management systems track CAC and call quality failures, key for voice/video troubleshooting.

D: Active synthetic probes proactively inject traffic to monitor loss, latency, and jitter under real-time conditions.

Why other options are incorrect:

B: Network convergence is not directly analyzed through call management tools.

E: Passive synthetic probes is not an accurate term; passive monitoring refers to analysis of real traffic flows, not synthetic tests.

F: PTP time-stamping is more applicable to clock synchronization, not regular voice/video performance monitoring.

E (Infrastructure ACLs): iACLs control what traffic can reach network infrastructure devices, directly securing the data plane.

G (Routing Protocol Authentication): Prevents malicious or spoofed routing updates which directly protect data plane routing decisions.

Why other options are incorrect:

A: Warning banners are management plane hardening.

B: Redundant AAA is management/control plane hardening.

C: CPPr protects the control plane.

D: SNMPv3 secures management plane.

F: Disabling unused services typically applies to management plane or control plane, not data plane.

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C (More consistent device configuration):Centralized control allows uniform policy application, eliminating configuration drift across devices.

E (Configure features at network-level rather than device-level):Controller-based networks abstract network services from individual devices, enabling network-wide configuration from a single source of truth.

Other options explained:

A: Forwarding tables still exist in both architectures.

B: Traditional networks offer per-device flexibility; controllers abstract this.

D: APIs are usually provided at controller level, not per device.

Software-Defined Networking (SDN) architecture is based on the logical decoupling of the control and data planes. According to the SDN reference model, the architecture typically includes the following planes:

Control Plane: This resides in the SDN controller and is responsible for decision-making, including route and policy calculations.

Application Plane: This layer contains business and network applications (e.g., firewalls, QoS policies) that communicate with the controller to request services and enforce policy.

These planes are essential in SDN architecture:

The control plane programs the forwarding behavior of network elements.

The application plane interacts via northbound APIs to define intent and service logic.

Options such as “Software plane” and “Network plane” are vague or not used in the SDN context. The “Management plane” is a separate functional layer and is not part of the architectural definition core to SDN as per CCDE v3.1.

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