Which action describes how a Cisco switch builds its MAC address table?

• A. Using the source MAC addresses of frames to build and maintain a MAC address table
• B. Building a routing table based on the first IP address in the frame header
• C. Forwarding frames with unknown destination IP addresses to the default gateway
• D. Utilizing the MAC address table to forward frames via the destination MAC address

Answer: (A)

A switch learns where devices are by listening to the source MAC addresses on frames it receives. Each time a frame arrives on a port, the switch notes the frame’s source MAC address and records that MAC as reachable via that port. Over time, this builds a MAC address table that maps each device’s MAC to the port where it was seen. This is how the switch knows where to forward future frames destined for that MAC.

That’s why the correct action is describing building and maintaining the MAC address table from source MACs. The other options describe routing decisions or IP-related behavior, which belong to Layer 3 functionality or to forwarding decisions after the MAC table is already built, not to how the MAC table itself is constructed.