What is Port Address Translation PAT?

Understanding Port Address Translation PAT

An extension to NAT to translate all addresses to one routable IP address and translate the source port number in the packet to a unique value. PAT also called NAT overload is a technique that allows multiple devices on a private network to share a single public IP address by using different port numbers to distinguish between different connections. This conserves scarce IPv4 addresses and provides a basic level of obscurity for internal systems. PAT is defined in RFCs related to NAT including RFC 3022 and addressed in network security frameworks. Organizations implement PAT through properly configured firewalls routers and security monitoring to track the relationship between internal and external connections. For example a small business might implement PAT on their internet router allowing hundreds of internal devices with private IP addresses to share a single public IP address for internet connectivity while keeping track of which internal system initiated each connection through port number mapping. Related terms Network Address Translation NAT Private addressing Public IP address Port mapping IP conservation Firewall RFC 1918 addresses Internet gateway.