Network Address Translation

Network Address Translation

Network Address Translation (NAT) provides a mechanism for a privately addressed network to access registered networks, such as the Internet, without requiring a registered subnet address. This eliminates the need for host renumbering and allows the same IP address range to be used in multiple intranets.

With NAT, the privately addressed network (designated as "inside") continues to use its existing private or obsolete addresses. These addresses are converted into legal addresses before packets are forwarded onto the registered network (designated as "outside"). The translation function is compatible with standard routing; the feature is required only on the router connecting the inside network to the outside domain.

Translations can be static or dynamic in nature. A static address translation establishes a one-to-one mapping between the inside network and the outside domain. Dynamic address translations are defined by describing the local addresses to be translated and the pool of addresses from which to allocate outside addresses. Allocation is done in numeric order and multiple pools of contiguous address blocks can be defined.