ZyXEL Communications p-2612HNU-FX User Manual

Chapter 8 Network Address Translation (NAT)

P-2612HNU-Fx User’s Guide

NAT translates the destination address (the inside global address) back to the 
inside local address before forwarding it to the original inside host.

A port forwarding set is a list of inside (behind NAT on the LAN) servers, for 
example, web or FTP, that you can make visible to the outside world even though 
NAT makes your whole inside network appear as a single computer to the outside 
world.

 for advanced technical information on NAT.

Use the Port Forwarding screen to forward incoming service requests to the 
server(s) on your local network.

You may enter a single port number or a range of port numbers to be forwarded, 
and the local IP address of the desired server. The port number identifies a 
service; for example, web service is on port 80 and FTP on port 21. In some 
cases, such as for unknown services or where one server can support more than 
one service (for example both FTP and web service), it might be better to specify 
a range of port numbers. You can allocate a server IP address that corresponds to 
a port or a range of ports.

The most often used port numbers and services are shown in 

. Please refer to RFC 1700 for further information about port numbers. 

Note: Many residential broadband ISP accounts do not allow you to run any server 

processes (such as a Web or FTP server) from your location. Your ISP may 
periodically check for servers and may suspend your account if it discovers any 
active services at your location. If you are unsure, refer to your ISP.

Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (A in 
the example), port 80 to another (B in the example) and assign a default server IP 
address of 192.168.1.35 to a third (C in the example). You assign the LAN IP