Guys,

I am a little confused, if you are using Exchange on an SBS box why are you using opendns or even the 2820 routers dns for forwarders??

The best way I have at home and that I install at all my clients is to use root hints and no forwarders, that way YOU are responsible for your own DNS lookups. This runs perfectly for me using sbs2008, I am using a 2820n with 3.3.2.1 FW and have no DNS problems using root hints, as long as your server has plenty of ram I think you'll even find you run quicker on your dns lookups as well. There is a benefit in the form of Opendns or any other Recursive DNS provider can't track your browsing habbits as well. (I know this matters to some people).

Regards John

I know it's an old thread but we've got exactly the same issue on several firmware versions up to and including 3.3.3

Some DNS lookups can cause the Router to either lock up or reboot (sometimes continuously).
From our testing it only seems to be when SYSLOG is enabled though.

As soon as you turn it off, you can do any bizarre DNS lookup you want and the Router is fine.