Quick Reference Guide

Reference Guide for the Model RT338 ISDN Router
Introduction 1-13
Single IP Address Operation Using NAT
In the past, if you needed multiple PCs on a LAN to access the Internet simultaneously, you would
have to obtain a range of IP addresses from the Internet service provider (ISP). This type of
Internet account is more costly than a single-address account typically used by a single user with a
modem rather than a router. The Model RT338 router employs an address-sharing method called
Network Address Translation (NAT). This method lets several networked PCs share an Internet
account using only a single IP address, which may be statically or dynamically assigned by your
ISP.
The router accomplishes address sharing by translating the internal LAN IP addresses to a single
address that is globally unique on the Internet. The internal LAN IP addresses can be either private
addresses or registered addresses. For more information about IP address translation, refer to RFC
1631, The IP Network Address Translator (NAT).
Figure 1-3 illustrates a single IP address operation.
Figure 1-3. Single IP Address Operation Using NAT
7786EA
192.168.0.2
192.168.0.3
192.168.0.4
192.168.0.5
192.168.0.1 172.21.15.105
Private IP addresses
assigned by user
Internet
IP addresses
assigned by ISP