Netopia 3300 - Manual (Page 98)

4-2 Firmware User Guide
Features
MultiNAT features can be divided into several categories that can be used simultaneously in different
combinations on a per-Connection Profile basis.
The following is a general description of these features:
Port Address Translation
The simplest form of classic Network Address Translation is PAT (Por t Address Translation). PAT allows a group
of computers on a LAN, such as might be found in a home or small office, to share a single Internet connection
using one IP address. The computers on the LAN can sur f the Web, read e-mail, download files, etc., but their
individual IP addresses are never exposed to the public network. Instead, a single IP address acts as the
source IP address of traffic originating from the LAN. The Netopia Router allows you to define multiple PAT
mappings, which can be individually mapped to different public IP addresses. This offers more control over the
access permitted to users on the LAN.
A limitation of PAT is that communication must be initiated from the internal network. A user on the external
side cannot access a machine behind a PAT connection. A PAT enhancement is the ability to define multiple PAT
mappings. Each of these can optionally map to a section or range of IP addresses of the internal network. PAT
mapping allows only internal users to initiate traffic flow between the internal and external networks.
Server lists
Ser ver lists, sometimes known as expor ted ser vices, make it possible to provide access from the public
network to hosts on the LAN. Ser ver lists allow you to define par ticular ser vices, such as Web, ftp, or e-mail,
which are available via a public IP address. You define the type of ser vice you would like to make available and
the internal IP address to which you would like to provide access. You may also define a specific public IP
address to use for this ser vice if you want to use an IP other than the WAN IP address of the Netopia Router.
Static mapping
If you want to host your own Website or provide other Internet ser vices to the public, you need more than
classic NAT. The reason is noted under Por t Address Translation above – external users cannot initiate traffic to
computers on your LAN because external users can never see the real addresses of the computers on your
LAN. If you want users outside your LAN to have access, for example, to a Web or FTP ser ver that you host, you
need to make a public representation of the real IP addresses of those ser vers.
Static mappings are a way to make one or more private IP addresses fully accessible from the public network
via corresponding public IP addresses. Some applications may negotiate multiple TCP connections in the
process of communication, which often does not work with traditional PAT. Static mapping offers the ability to
use these applications through NAT. Each private IP address is mapped, on a one-to-one basis, to a public IP
address that can be accessed from the Internet or public network. As with PAT mappings, you may have multiple
static mappings to map a range of private IP addresses to a range of public IP addresses if desired.