The combination modem/router is one of the devices supplied by Comcast's Internet service. Due to the custom firmware, the device does not permit any changes to the DNS server settings. This is based from the support article for this particular model:
What's the next step?
There are a few options to explore:
- Contact Comcast or Technicolor support to confirm if your device supports changes made to the DNS server settings. There's a possibility that Comcast may be able to release the device from its restrictions upon request.
- If Comcast or Technicolor cannot assist you with the device, your computers can be configured using the steps at https://support.opendns.com/forums/21618384-Computer-Configuration. This is as effective as using your router, but you'll need to set up your computer's manually with the above instruction set.
I still want to use a router.
This is one of the most requested options for configuring OpenDNS, because it can filter all computers and smart devices without modifying each setting individually. The alternative to the above options is to set up a second router to your network, and configure that device with our steps at https://support.opendns.com/categories/20080020-OpenDNS-Device-Configuration. This will act as the gateway for your home, and all the requested domains will be routed to OpenDNS.
RECOMMENDED: To make sure that the second router is the only device users can connect to, it's recommended to change the Tecnicolor's WiFi password and hide the WIFi name from being broadcasted. On page 30, in the above manual, offers steps for changing the password.
To ensure that the router is secured, the Technicolor's admin password can be changed. On page 28, there are steps on how to change the password that is required to access the router's settings.