Draytek Vigor2920 Series User Manual page 189

Private IP
Private Port
After finishing all the settings here, please click OK to save the configuration.
Note that the router has its own built-in services (servers) such as Telnet, HTTP and FTP etc.
Since the common port numbers of these services (servers) are all the same, you may need to
reset the router in order to avoid confliction.
For example, the built-in web user interface in the router is with default port 80, which may
conflict with the web server in the local network, http://192.168.1.13:80. Therefore, you need
to change the router's http port to any one other than the default port 80 to avoid conflict,
such as 8080. This can be set in the System Maintenance >>Management Setup. You then
will access the admin screen of by suffixing the IP address with 8080, e.g.,
http://192.168.1.1:8080 instead of port 80.
Specify the private IP address of the internal host providing the
service. If you choose Range as the port redirection mode, you
will see two boxes on this field. Type a complete IP address in
the first box (as the starting point) and the fourth digits in the
second box (as the end point).
Specify the private port number of the service offered by the
internal host.
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Vigor2920 Series User's Guide