PortAdressTranslation

Port Address Translation (PAT) is a network address translation (NAT) technique that allows multiple devices on a local network to share a single public IP address for internet access. Unlike traditional NAT, which maps one-to-one IP addresses, PAT maps multiple private IP addresses to a single public IP address using different port numbers. This is achieved by appending a port number to the public IP address, creating a unique identifier for each communication session.

PAT is commonly used in residential and small business networks to conserve public IP addresses, which are in short supply. It is also used in larger networks to provide additional security by hiding the internal network structure from external entities. PAT operates at the transport layer of the OSI model, typically using protocols like TCP and UDP.

The process of PAT involves the following steps:

1. When a device on the local network initiates a connection to an external server, the PAT device (such as a router) intercepts the request.

2. The PAT device modifies the source IP address to the public IP address and assigns a unique port number to the connection.

3. The modified packet is then sent to the external server.

4. The external server responds to the public IP address and port number.

5. The PAT device receives the response, identifies the corresponding internal device using the port number, and forwards the response to the appropriate device.

PAT has several advantages, including IP address conservation, enhanced security, and the ability to support multiple devices on a single public IP address. However, it also has limitations, such as the potential for port conflicts and the requirement for devices to support PAT-compatible protocols. Additionally, PAT can introduce complexity in network troubleshooting and management.