When trying to set up the router to use a specific DNS server (OpenDNS, etc), not automatically provided by the ISP, the admin interface has "Use These DNS Servers" grayed out and not selectable unless the IP adress is set to "Use Static IP Address" first.
In order to use a dynamic IP address provided by the ISP, you need to disable Circle (Advanced->Security->Parental Controls). Then you can set your specific DNS with automatic IP address. Once that's set up, you can go back and re-enable Cicle. The DNS / IP settings will remain. I don't know why Cicle would force that interaction, but the resolution is easy.
