Network/Port address translation

NAT/PAT

Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. 

NAT serves three main purposes:

Provides a type of firewall by hiding internal IP addresses

Enables a company to use more internal IP addresses. Since they're used internally only, there's no possibility of conflict with IP addresses used by other companies and organizations.

Allows a company to combine multiple ISDN connections into a single Internet connection.

Port address translation is a type of network address translation. During PAT, each computer on LAN is translated to the same IP address, but with a different port number assignment.

PAT is also referred to as overloading, port-level multiplexed NAT or single address NAT. 

In addition to the advantages provided by NAT:

• PAT (Port Address Translation) allows many internal hosts to share a single external IP address.
• Users who do not require support for inbound connections do not consume public IP addresses.