It seems that you are having some issues trying to set up your Slingbox AV for Internet Viewing with the D-Link DIR-825 router.
Even though you own the Slingbox AV, the following link will provide you with the steps to follow in order to set up your Slingbox for Internet Viewing.
The following third-party link will provide you with the steps to follow in order to know the adjustments to apply on your D-Link router.
If the issue persists after applying these adjustments, I recommend you to verify if you have a multiple router network (sometimes, your modem will also work as a router). If this is your case, I encourage you to check this link.