DNS conflict between Comcast and Dyndns
Comcast want their users use their safe DNS:
75.75.75.75
75.75.76.76
DynDns wants their clients to use theirs:
216.146.35.35
DynDns’s client application automatically changes to the DNS to their address, and Comcast’s Constant Guard wants to change it back. It seems that DynDns always wins, but Constant Guard keeps popping up warning for this. The way to solve it is to:
DynDNS client app>Advanced>Uncheck "Enable DynDNS.com Internet Guide on this PC"
(Originally written before 2018)