> I have been trying to assist someone with a business connection that runs a server farm.  Recently the business cable modem started to short-stop port 53 for UDP and TCP.  Apparently, a transparent DNS proxy somehow got activated and all outbound traffic to any IPv4 or IPv6 address is intercepted and handled by the modem – or not handled. 

Sounds like the person you helped turned on Security Edge. They can turn it off too at https://business.comcast.com/support/article/internet/securityedge-manage-settings.

Jason