What does Port Address Translation (PAT) do in a network?

Port Address Translation (PAT) plays a crucial role in managing IP address space, especially in environments where many devices need to connect to the internet using a limited number of public IP addresses. PAT works by allowing multiple devices on a local network to be represented by a single public IP address while using different source port numbers to maintain unique sessions.

When a device on the local network initiates a connection to the internet, PAT translates the internal IP address of that device and assigns a unique source port number to it. This means that when the traffic is sent out, multiple devices can share the same public IP address, distinguishing their sessions through these unique port numbers. When responses come back from external servers, the router or firewall uses the port numbers to direct the incoming packets to the appropriate internal device.

This mechanism efficiently conserves IP addresses while enabling successful communication between many devices and the broader internet, making it a key function in network address translation scenarios. The capability of PAT to modify source port numbers ensures that each connection can be tracked and maintained distinctly, allowing seamless connectivity for numerous devices.