Which statement about a switch learning MAC addresses is true?

Which statement about a switch learning MAC addresses is true?

• A. It learns MAC addresses by inspecting source frames on each port.
• B. It uses DNS queries to map IP to MAC.
• C. It requires manual configuration for each port.
• D. It operates only at layer 3.

Answer: (A)

MAC address learning happens as frames arrive on a switch port. The switch reads the source MAC address in each frame and records that this MAC is reachable via the port where the frame came in, building a MAC address table. When a frame with a known destination MAC arrives, the switch forwards it only to the specific port associated with that MAC; if the destination MAC hasn’t been seen yet, the switch floods the frame to all ports except the source. This automatic learning is what lets the switch efficiently forward traffic without manual entry. DNS queries and IP-to-MAC mappings are not used by switches to forward frames, since DNS is a domain-name system and IP-to-MAC mappings are handled by ARP at Layer 3, not by the switch’s learning process. While static MAC entries can be configured, normal operation relies on automatic learning, and switches operate primarily at Layer 2, not Layer 3.

MAC address learning happens as frames arrive on a switch port. The switch reads the source MAC address in each frame and records that this MAC is reachable via the port where the frame came in, building a MAC address table. When a frame with a known destination MAC arrives, the switch forwards it only to the specific port associated with that MAC; if the destination MAC hasn’t been seen yet, the switch floods the frame to all ports except the source. This automatic learning is what lets the switch efficiently forward traffic without manual entry. DNS queries and IP-to-MAC mappings are not used by switches to forward frames, since DNS is a domain-name system and IP-to-MAC mappings are handled by ARP at Layer 3, not by the switch’s learning process. While static MAC entries can be configured, normal operation relies on automatic learning, and switches operate primarily at Layer 2, not Layer 3.