How NAT Works

DSL-504 ADSL Router User’s Guide

network (but not on the Internet) and vice-versa. The Router allows up to 253 host IP addresses.

NAT has two major benefits. First, NAT allows many users to access the Internet using a single global IP address. This can greatly reduce the costs associated with Internet access and also helps alleviate the current shortage of Internet IP addresses. Secondly, the NAT process creates a firewall, which hides your local network from Internet users, providing a degree of security to your Internet connection.

To be successfully implemented, NAT should be used only when the majority of network traffic remains on the local network. In cases where a large percentage of network traffic is destined for the Internet, NAT can adversely affect the speed and performance of your Internet connection. Network servers such as ftp servers, web servers or mail servers should use the port redirection capabilities of the Router.

NAT will work in conjunction with DHCP and Port Redirection. Thus, if both are enabled and properly configured, the DHCP server in the DSL-504 will assign local IP addresses to computers on your network. The Port Redirection feature allows an administrator to direct specific types of incoming packets to another server or designated host. For example, a common way to use Port Redirection would be to direct incoming HTTP packets (through TCP logical port 80) and redirect them to an HTTP server (conventionally through port 8080).

In the most common NAT configuration, your network uses local IP addresses that are not valid on the Internet. Each Internet (global) IP address is unique. Your network administrator can assign local IP addresses on your network (within guidelines defined later in this chapter and in “Appendix B, IP Concepts”). This can be done manually or by using DHCP. The WAN port on the router is assigned a globally unique public IP Address that is valid on the Internet, since it will be sending and receiving data directly to the Internet and is therefore part of it. Please study the example diagram below carefully.