Describe how a computer uses its ARP table and the ARP protocol when preparing to transmit a packet to the local network.

What will be an ideal response?

When a computer prepares to transmit a packet to a destination on the local network, it checks its ARP table for an IP-to-MAC address resolution for the destination node. If the computer finds the address resolution, the source computer uses the information to create the Data Link header with the source and destination MAC addresses. The packet is then sent directly to the destination node on the local network.

If the source computer does not find an entry for the destination computer's IP address in its ARP table, it sends an ARP broadcast to the local subnet in an attempt to discover the destination computer's MAC address. Because the destination address in this discovery packet is a broadcast (FF-FF-FF-FF-FF-FF), every host on the local subnet must process the packet to determine if it is "of interest." When the packet reaches the Network layer, where ARP is processed, the host can determine if its own IP address is being specified in the ARP broadcast packet. Only the correct host responds; the others discard the packet. The host that discovers its IP address in the broadcast packet responds to the source computer's ARP request by providing its MAC address.