ZyXEL Communications VMG1312-B10A - 11.2 The Port Forwarding Screen

Chapter 11 Network Address Translation (NAT)
VMG1312-B Series User’s Guide
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WAN side. When t he response com es back, NAT translates t he destination address ( t he inside
global address) back t o the inside local address before forwarding it to t he original inside host .
Port Forwarding
A port forwarding set is a list of inside ( behind NAT on t he LAN) servers, for exam ple, web or FTP,
that you can m ake visible t o the outside world even though NAT m akes your whole inside network
appear as a single com puter to the outside world.
Finding Out More
See
Section 11.8 on page 196 for advanced t echnical inform at ion on NAT.
11.2 The Port Forwarding Screen
Use t he Port For w ar ding screen t o forward incom ing service request s t o t he ser ver( s) on your
local network.
You m ay ent er a single port num ber or a range of port num bers to be forwarded, and the local I P
address of t he desired server. The port num ber ident ifies a service; for exam ple, web service is on
port 80 and FTP on port 21. I n som e cases, such as for unknown services or where one server can
support m ore than one service (for exam ple bot h FTP and web service), it m ight be bet ter to
specify a range of port num bers. You can allocat e a server I P address that corresponds t o a port or
a range of ports.
The m ost oft en used port num ber s and services are shown in
Appendix F on page 359. Please refer
to RFC 1700 for further inform at ion about port num bers.
Note: Many resident ial broadband I SP account s do not allow you t o run any server
processes ( such as a Web or FTP server) from your locat ion. Your I SP m ay
periodically check for servers and m ay suspend your account if it discovers any
active services at your location. I f you are unsure, refer to your I SP.
Configuring Servers Behind Port Forwarding (Example)
Let's say you want to assign port s 21-25 t o one FTP, Telnet and SMTP server (A in the exam ple),
port 80 to anot her (B in the exam ple) and assign a default server I P address of 192.168.1.35 t o a