Question

If a mapping for a local destination host is not found in a source host ARP cache, how does the source host send an ARP request?

A) Broadcasts an ARP request on the local network
B) Sends a unicast ARP request to the destination host
C) Queries the DNS server for host information
D) Waits for an automatic ARP update

Answer 1

When a source host does not have the ARP mapping for a local destination host, it broadcasts an ARP request on the local network. Every host receives this request, but only the intended destination host responds with an ARP reply containing its MAC address.

Step-by-step explanation:

If a mapping for a local destination host is not found in a source host ARP cache, the source host sends an ARP request by broadcasting it on the local network. This is typically done using a special packet that is sent to the physical network broadcast address, which in the case of an Ethernet network, would reach all hosts within the same broadcast domain. The ARP request contains the IP address of the destination host and asks for the corresponding MAC address. Every host in the network receives this ARP request, but only the host with the matching IP address will reply with an ARP reply, providing its MAC address. This information is then cached by the source host for future packets to the destination host.