Unfortunately, questions like as VPN is not covered in the product data sheet or technical manual, and in the time that I was searching about this router, this point was not covered. Before to acquire this router, I had another old router (another brand), and this old router didn't have any issues regarding on VPN, so I thought the newest products, like as DIR-615, would work like my old router, but with more feature, like as "N" support. Sure, if I found any comment regarding this kind of issue, I never had bought. But unfortunately many issues just appear when somebody try to apply to a specific application. I understood that this kind of products can show issues along the time, but it's important that the manufacturer opens his mind and has for wish to fix it.
I'm understanding the game, I disagree but I respect.
I hope that in the future, DLINK comes to change this way, and assume the responsability to fix issues and not let this responsability to independent group.