Network and Address Terms

The NAT implementation defines an address realm as either inside or outside, with the router that is running NAT acting as the defining boundary between the two realms.

From a NAT perspective, an inside network is the local portion of a network that uses private, not publicly routable, IP addresses that you want to translate. An outside network is the public portion of a network that uses legitimate, publicly routable IP addresses to which you want private hosts to connect.

The terms in this section relate to those addresses you want to translate from one network realm to another. Addresses within these realms are labelled as either local or global.

When reading the following sections, keep the following in mind:

• The terms inside and outside refer to where a host resides
• The terms local and global refer to where the address appears on the NAT network.

Inside Local Addresses

The inside local address is a configured IP address that is assigned to a host on the inside network. Addresses may be globally unique (not requiring translation), allocated from the private address space defined in RFC 1918, or officially allocated to some other organization.

Inside Global Addresses

The inside global address is the "translated" IP address of an inside host as seen by an outside host and network. Addresses may be allocated from a globally unique address space (often provided by the ISP, if the inside address is connected to the global Internet).

Outside Local Addresses

The outside local address is the "translated" IP address of an outside host as it appears to the inside network. Addresses may be globally unique (not requiring translation), allocated from the private address space defined in RFC 1918, or officially allocated to some other organization.

Outside Global Addresses

The outside global address is the configured, publicly routable IP address assigned to a host on the outside network.