You will need to forward a port. Use Port 6346 1st you will need to set up a static ip. I'm not sure which model applies to you 624 or 624+ so I've provided both instructions: Step 1:
(a) Setting up a Static IP Address with the Dlink DI-624 OR Setting up a Static IP Address with the Dlink DI-624+

(b) Port Forwarding for the Dlink DI-624
OR Port Forwarding for the Dlink DI-624+

2. Force IP within LW: Force IP instructions & sample image

This should do the job. I use a d-link modem router which I must reboot after those changes but I don't know about your model.. But don't forget to save your settings anyway.