Port numbering and well-known port numbers / Example of multiple sessions between hosts

Port numbering and well-known port numbers

10.2.4 This page will discuss the three categories of port numbers.

Port numbers are represented by 2 bytes in the header of a TCP or UDP segment. This 16-bit value can result in port numbers ranging from 0 to 65535. The three categories of port numbers are well-known ports, registered ports, and dynamic or private ports. The first 1023 ports are well-known ports. These ports are used for well-known network services such as FTP, Telnet, or DNS. 

Registered ports range from 1024 to 49151. Ports between 49152 and 65535 are defined as dynamic or private ports.

The Interactive Media Activity will help students become more familiar with port numbers.

The next page will give an example of multiple sessions.

Example of multiple sessions between hosts 

10.2.5 This page will explain how 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 through port 23 and an Internet connection through port 80. The IP and the MAC addresses would be the same because the packets are received 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.

In the Lab Activity, students will enable HTTP on a router and observe well-known ports.
The next page will discuss the three types of addresses.