The user of Host1 wants to ping the DSL modem/router at 192.168.1.254. Based on the Host1
ARP table that is shown in the exhibit, what will Host1 do?

A.
send a unicast ARP packet to the DSL modem/router

B.
send a Layer 2 broadcast that is received by Host2, the switch, and the DSL modem/router

C.
send Layer 3 broadcast packets to which the DSL modem/router responds

D.
send unicast ICMP packets to the DSL modem/router

Explanation:
Address Resolution Protocol (ARP) is a network protocol, which maps a network layer protocol
address to a data link layer hardware address. For example, ARP is used to resolve IP address to
the corresponding Ethernet address.
A host in an Ethernet network can communicate with another host, only if it knows the Ethernet
address (MAC address) of that host. The higher level protocols like IP use a different kind of
addressing scheme (like IP address) from the lower level hardware addressing scheme like MAC
address. ARP is used to get the Ethernet address of a host from its IP address. ARP is extensively
used by all the hosts in an Ethernet network.
In this case, there is already an entry for this IP address, meaning the this host already knows the
MAC to IP address mapping for this destination so there is no need to send out an ARP request;
instead it will send the ICMP packet directly to 192.168.1.254 via unicast.