Technical Reference; Natport Forwarding: Services And Port Numbers; Nat Port Forwarding Example - ZyXEL Communications NBG417N User Manual

Chapter 11 NAT
Table 48 Network > NAT > Advanced
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11.5 Technical Reference

The following section contains additional technical information about the NBG4115
features described in this chapter.

11.5.1 NATPort Forwarding: Services and Port Numbers

A port forwarding set is a list of inside (behind NAT on the LAN) servers, for
example, web or FTP, that you can make accessible to the outside world even
though NAT makes your whole inside network appear as a single machine to the
outside world.
Use the Application 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.
In addition to the servers for specified services, NAT supports a default server. A
service request that does not have a server explicitly designated for it is forwarded
to the default server. If the default is not defined, the service request is simply
discarded.
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.

11.5.2 NAT Port Forwarding Example

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
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