If the switch receives a frame and the source MAC address is not in the MAC address table, what action occurs?

• A. The switch adds it to its MAC address table associated with the port number.
• B. The switch shares the MAC address table entry with any connected switches.
• C. The switch refreshes the timer on that entry.
• D. The switch forwards the frame to all ports.

Answer: (A)

MAC address learning is being tested here. When a switch receives a frame and the source MAC address isn’t yet in its MAC address table, it learns that address by recording which port the frame came from. The switch creates an entry that maps the source MAC to the ingress port, so future frames destined for that MAC can be forwarded directly to that port instead of flooding. This dynamic learning is fundamental to efficient switching, and entries typically age out after a timeout if there’s no activity.