If a host's ARP cache has no mapping entry for a destination on a remote network, to what destination MAC address will the ARP request be sent?

If a host's ARP cache has no mapping entry for a destination on a remote network, to what destination MAC address will the ARP request be sent?

• A. Broadcast MAC address
• B. The destination host's MAC address
• C. The router's MAC address
• D. The host's own MAC address

Answer: (A)

When a host needs to reach a destination on a different network, it sends the packet to its default gateway. If the gateway’s MAC address isn’t in the ARP cache, the host asks for it by issuing an ARP request. Since the request can’t be delivered to a single unknown device on the local segment, it’s broadcast to everyone on the local network. The Ethernet destination is the broadcast MAC address (ff:ff:ff:ff:ff:ff), so all devices hear the request, and only the device with the gateway IP will reply with its MAC. With that MAC, the host can forward the packet to the router.

When a host needs to reach a destination on a different network, it sends the packet to its default gateway. If the gateway’s MAC address isn’t in the ARP cache, the host asks for it by issuing an ARP request. Since the request can’t be delivered to a single unknown device on the local segment, it’s broadcast to everyone on the local network. The Ethernet destination is the broadcast MAC address (ff:ff:ff:ff:ff:ff), so all devices hear the request, and only the device with the gateway IP will reply with its MAC. With that MAC, the host can forward the packet to the router.