DLink DIR 655 Port Forward baffling issue

[Stationwest]

Hello all, here is my most baffling issue. I have a surveillance DVR and I'm trying to access it remotely. I log in to the router, and PF the appropriate IP and port to the public internet. Of course When I test it I am in the building but connecting to the DVR via my public internet IP and port. This is to say I am routing through the public internet and then back into my router, through port 80 and into the DVR.

 

This works fine on site.... as soon as I leave the premise and try to connect VIA a different internet connection, using the same public internet IP and port I was using on site, I no longer have access. I am perplexed as to why I can access the DVR in the building even though I am accessing it from my external IP but not at home.

 

If anyone can shed any light on this issue, I would be supper happy, and probably send you a virtual case of beer!

 

Cheers!

 

-AW-