To forward a frame toward its destination on a switch, which address does the switch consult in the frame header?

• A. The switch forwards to all ports regardless of MAC table
• B. The switch forwards the frame using the source MAC address
• C. The switch forwards based on IP header
• D. The switch forwards the frame using the destination MAC address from the frame header

Answer: (D)

Forwarding decisions on a switch are based on the destination MAC address found in the Ethernet frame header. The switch uses its MAC address table (CAM table) to map each learned MAC to the port where that host is reachable. When a frame arrives, it looks up the destination MAC in the table and, if known, forwards the frame only to the corresponding port. If the destination isn’t in the table, the switch floods the frame to all ports in the same VLAN (except the ingress port). The source MAC is learned from the frame to update the table for future traffic. IP addresses are part of the layer above and aren’t used by a basic Layer 2 switch for forwarding.