To understand how communication is successful in the network, it is important to understand the roles of both the network layer addresses and the data link addresses when a device is communicating with another device on the same network. In this example we have a client computer, PC1, communicating with a file server, FTP server, on the same IP network.

Network Addresses

The network layer addresses, or IP addresses, indicate the network and host address of the source and destination. The network portion of the address will be the same; only the host or device portion of the address will be different.

Data Link Addresses

When the sender and receiver of the IP packet are on the same network, the data link frame is sent directly to the receiving device. On an Ethernet network, the data link addresses are known as Ethernet MAC addresses. MAC addresses are 48-bit addresses that are physically embedded on the Ethernet NIC. A MAC address is also known as the physical address or burned-in address (BIA).

The source and destination addresses are added to the Ethernet frame. The frame with the encapsulated IP packet can now be transmitted from PC1 directly to the FTP server.