A port is a 16-bit number that is used to identify a specific process running on a device. It is used in conjunction with the device's IP address to uniquely identify a specific network service, such as a web server or email server.
When a device sends data to another device on a network, the data is packaged into packets. Each packet contains the IP address of the destination device, and the port number that the data is intended for. The receiving device uses the IP address and port number to identify the specific process that the data is intended for, and passes the data to that process.
Ports are used by the Transport layer (TCP or UDP) to direct the data to the proper process on the host machine. Each process that wants to communicate over the network, bind itself to a unique port number on the host machine.
There are two types of ports:
- Well-known ports: These ports are assigned to common services, such as HTTP (port 80) and HTTPS (port 443), and are in the range of 0 to 1023.
- Ephemeral ports: These ports are assigned dynamically to client applications when they initiate a connection and are in the range of 1024 to 65535.
In summary, a port is a 16-bit number that is used to identify a specific process running on a device, it's used in conjunction with the device's IP address to uniquely identify a specific network service, such as a web server or email server, ports are used by the Transport layer to direct the data to the proper process on the host machine, and there are two types of ports: well-known ports and ephemeral ports.