Which two functions are performed at the core layer of the three-layer hierarchical network design model? (Choose two).

Question

Options

• AFault isolation
• BQos classification and marking boundary
• CFast transport
• DReliability
• ELoad balancing

Explanation

C (Fast transport) and D (Reliability) are the correct answers. The core layer is the high-speed backbone of the network, purpose-built for forwarding packets as quickly as possible with minimal latency - making fast transport its primary function. Reliability (via redundancy, high availability, and fault tolerance) is equally critical here because any core failure affects the entire network.

Why the distractors are wrong:

• A (Fault isolation) belongs to the distribution layer, which uses policies and boundaries to contain broadcast domains and contain failures.
• B (QoS classification and marking) is an access layer function - traffic should be classified and marked as close to the source as possible, not at the core.
• E (Load balancing) is also a distribution layer responsibility, where routing decisions and traffic policies are applied.

Memory tip: Think of the core as a highway - its only job is to move traffic fast and stay up. It doesn't make decisions (distribution does) or greet users (access does). If a feature sounds like "policy" or "filtering," it belongs lower in the hierarchy, not at the core.

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