Arris routers (often co-branded with Motorola) such as Surf Boards are typically distributed from Internet providers. Many of these routers have been modified such that their DNS settings cannot be modified which would make them not be able to be configured for OpenDNS.
If your Arris router was supplied by your Internet Provider (i.e. Comcast, Time Warner), you may need to confirm with the provider if their device supports setting the DNS settings on the router.
We're still building a list of Arris routers that are capable of changing DNS servers. If you're unsure, visit http://support.opendns.com and submit a support request with your Arris router's model number and the Internet Provider that you got the device from so that we may check into it.
A full list of Comcast DOCSIS 3.0 routers can be found here: http://mydeviceinfo.comcast.net/ (Please note that not all of the routers listed there can support configuration for OpenDNS)