Messages

I am trying to block all websites except a couple for a client that wants opnsense on it.  He has asked me to block all websites except two sites related to his business.  Considering that dns could return so many different IPs for any site, is squid able to do this type of web filtering or do I need research dns filtering?  This extreme blocking is the first time I am doing it for a site that can have upwards of 20+ computers and I am not sure there is a good solution to achieve that.  Anybody done such a thing?  Would appreciate the advise.  Thanks