A device that connects to multiple networks has the IP addresses of multiple networks. You cannot directly use the IP addresses mentioned earlier for the following reasons:
An IP address is the network layer address of a host. Before a datagram is transmitted to the destination host, the physical address of the host must be obtained. Therefore, the IP address must be first resolved into a physical address.
To remember a host name is easier than to remember an IP address. Therefore, the host name needs to be resolved into an IP address.
Figure 1 shows the relationship between a host name, an IP address, and a physical address. On the Ethernet, the physical address of a host refers to the MAC address. The DNS server resolves a host name into an IP address. The Address Resolution Protocol (ARP) resolves the IP address into a MAC address.
Figure 1 Relationship between the host name, IP address, and physical address
