In a typical inter-subnet communication, what is the destination MAC address used in the Ethernet frame?

• A. Destination MAC address of the destination host
• B. Destination MAC address of the next-hop router
• C. Broadcast MAC address
• D. Source MAC address

Answer: (B)

Inter-subnet communication starts with delivering the frame to the local router. The sending host uses ARP to learn the MAC address of its default gateway on the local network, then encapsulates the IP packet in an Ethernet frame addressed to that gateway’s MAC. The router receives the frame, strips off the Ethernet header, and uses IP routing to send the packet toward the destination subnet. So, the destination MAC in the Ethernet frame is the MAC address of the next-hop router (the default gateway). It isn’t the final host’s MAC, it isn’t a broadcast, and it isn’t the source’s MAC, because on a different subnet the local delivery is to the gateway first.