Prevent users from defining DNS servers on client devices.

[cmcdonald]

I've always wondered how to do this:

My university utilizes a system that routes ALL traffic through OpenDNS regardless of what DNS servers are defined on client devices. For example, if I change the DNS servers on my laptop to 8.8.8.8, 8.8.4.4, my traffic still goes through OpenDNS. How are they accomplishing this? And is this possible on pfSense?

[JoelC707]

Probably via outbound firewall/NAT rules they are simply redirecting all outbound requests to UDP 53 to OpenDNs. This should be easily accomplished on pfSense as well.