Port numbers are used to track multiple sessions that can occur between hosts. The source and destination port numbers combine with the network address to form a socket. A pair of sockets, one on each host, forms a unique connection. For instance, a host might have a telnet connection, port 23, while at the same time be surfing the net, port 80. The IP and the MAC addresses would be the same because the packets are coming from the same host. Therefore, each conversation on the source side needs its own port number, and each service requested needs its own port number.

Lab Activity Lab Exercise: Well-Known Port Numbers and Multiple Sessions In this lab, the student will enable HTTP services on a router