Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addressesfor internal traffic and a second set of addresses for external traffic. A NAT boxlocated where the LAN meets the Internet makes all necessary IP address translations.

The technique was originally used for ease of rerouting traffic in IP networks without renumbering every host. It has become a popular and essential tool in conserving global address space allocations in face of IPv4 address exhaustion.

NAT serves three main purposes:

• Provides a type of firewallby 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.