I've had some DNS problems with DIR-827. Three laptops, each has a reserved local IP address. Two of them connect without any issues. But the remaining laptop was always a problem. Whenever it connected to the router, the router's DNS functionality was ruined. I could still ping any IP from the desktop, but there was no domain access. Rebooting the router while the laptop's wireless adapter was on did not help. When the wireless adapter was off, rebooting restored the DNS functionality.
After much experimenting, a solution was to untick the "Enable DNS Relay" under SETUP-->Network Settings-->Router Settings.
I am not sure how the client's wireless adapter can cause so much damage, but one weird thing about that laptop is that the default network has a name NULL (which I can't change, as that configuration is managed by employer).