Which set correctly lists the core functions of a network switch?

• A. Address learning, forward/filter decision, and loop avoidance
• B. Address learning, routing, and QoS
• C. Spanning tree, port mirroring, and load balancing
• D. Collision detection, token passing, and broadcast suppression

Answer: (A)

The essential task of a network switch is to learn where devices live on the network, forward or filter traffic accordingly, and keep the network from looping.

First, address learning happens as frames arrive. The switch notes the source MAC address and the port it came in on, building a MAC address table. This lets it map each device to a specific port, so future frames can be sent directly to the right place rather than broadcast everywhere.

Second, the forward/filter decision uses that MAC table to decide where to send each frame. If the destination MAC is known, the switch forwards the frame only to the corresponding port. If the destination is unknown, it floods the frame to all ports in the same collision domain to reach the device. This keeps traffic efficient and reduces unnecessary transmissions.

Third, loop avoidance is about preventing broadcast storms and multiple redundant paths from creating endless circulating frames. Protocols like Spanning Tree help by disabling some redundant paths, ensuring there’s a single stable path between devices.

While switches can offer features like routing between VLANs or quality-of-service enhancements, those are extra capabilities. The combination of address learning, forward/filter behavior, and loop avoidance best captures the primary duties of a switch.