As our name implies, OpenDNS is a DNS based service. Rather than having to install software, all our users need to do is make a configuration change to point their systems to our DNS resolvers. Unfortunately, not all Internet Service Providers (ISPs) allow the use of third-party DNS providers such as OpenDNS.
This most often comes into play with satellite, wireless, or 3G/4G mobile data ISPs, because their technology requires that you use specific transmitters for your connection. As such, their customers are often required to use their DNS providers to maintain the best connection to these transmitters. Known providers who cannot allow OpenDNS on their network include Wildblue and HughesNet.
The best way to tell if your ISP will not allow the use of third-party DNS providers is to ask them, but there are other ways you can determine this from your home.
A simple test is to go to https://dnsleaktest.com/ and check whether you're able to connect the OpenDNS servers with the Standard test. Note: you must have the OpenDNS servers already configured as your primary and secondary DNS servers.
There are other tests you can perform before changing your servers to OpenDNS, but you need to know how to use a Command Line Interface in your operating system.
Microsoft Windows (instructions on how to open Command Prompt can be found here)
Windows users can open up their Command Line and run the following command: nslookup -type=txt debug.opendns.com. 22.214.171.124
Apple Mac OS X (Instructions on how to open up Terminal can be found here)
OS X users can open up Terminal and run the following command: /usr/bin/dig @126.96.36.199 +time=10 debug.opendns.com txt
Linux (As there are many distributions of Linux, please consult documentation for your specific distro on how to get to the CLI.)
Linux users can open up their CLI and run the following command: nslookup -type=txt debug.opendns.com. 188.8.131.52
If third-party DNS providers aren't allowed on your network, the response from the server will generally look like the following:
Results for: nslookup -timeout=10 -type=txt debug.opendns.com. 184.108.40.206
stderr:*** resolver1.opendns.com can't find debug.opendns.com.: Non-existent domain
The debug.opendns.com server will only respond to requests made using our DNS servers (220.127.116.11 and 18.104.22.168). If the request is denied when explicitly made with those servers, the most likely cause is that the ISP will not allow the request to be transmitted at all, resulting in the "non-existent domain" error.
If your ISP says that you can use third-party DNS providers, but you aren't sure that you're using our service, please open up a support ticket with the results of this Diagnostic Tool and we'll be happy to assist you.