D-Link DSL-2750B User Manual page 56

Section 3 - Configuration
Select a Service drop-down menu for a pre-configured application or
select Custom Server type a name input box to define your own
application.
The External Port shows the ports opened for remote users in the WAN
side of the router. The TCP/UDP means the protocol type of the opened
ports.
The Internal Port shows the ports opened in the PC with the appointed IP
Address. The TCP/UDP means the protocol type of the opened ports.
Please click the Apply button to save the configuration.
D-Link DSL-2750B User Manual 56