300-320 Question #165: Real Exam Question with Answer & Explanation

The correct answer is A: Layer 3 link between distribution switches. A Layer 3 (routed) link between distribution switches eliminates Layer 2 adjacency between them, removing the possibility of a bridging loop at that tier and making convergence deterministic through routing protocol timers rather than STP. VLANs that do not span access switches (

Question

A network engineer must create a Layer 2 switch block design that has deterministic convergence and is loop-free at Layer 2. Which two switch block elements are needed to meet the requirements? (Choose two.)

Options

ALayer 3 link between distribution switches
BHSRP with interface tracking on uplinks to core switches
CRPVST with equal bridge priority on distribution switches
DVLANs that do not span access switches
ELayer 2 link between distribution switches

Explanation

A Layer 3 (routed) link between distribution switches eliminates Layer 2 adjacency between them, removing the possibility of a bridging loop at that tier and making convergence deterministic through routing protocol timers rather than STP. VLANs that do not span access switches (i.e., each VLAN is local to a single access switch) prevent inter-switch VLAN dependencies that would force STP to arbitrate loops across the distribution tier. Together, these two design choices confine any potential L2 domain to a single access switch and a single uplink path to distribution, making the topology inherently loop-free without relying on STP for convergence. A Layer 2 link between distribution switches (option E) would reintroduce loops requiring STP, and RPVST with equal priority (option C) does not eliminate loops-it simply elects a root, which is non-deterministic when priorities are equal.

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