The Frontier website stopped resolving for me, turned out to be comcast DNS.
It was working a day or two ago, so I don't know what happened for them to just "forget" about the site. Switching to google DNS resolved the problem. If you're on comcast and unable to access the frontier forums, switch to 8.8.8.8 and 8.8.4.4 for your DNS to get it working again.
> server 8.8.8.8 Default Server: google-public-dns-a.google.com Address: 8.8.8.8
> www.frontier.co.uk Server: google-public-dns-a.google.com Address: 8.8.8.8
Non-authoritative answer: Name: www.frontier.co.uk Address: 83.222.231.12
> server 75.75.75.75 Default Server: cdns01.comcast.net Address: 75.75.75.75
> www.frontier.co.uk Server: cdns01.comcast.net Address: 75.75.75.75
*** cdns01.comcast.net can't find www.frontier.co.uk: Server failed
Posted Jan 3, 2016, 3:30 PM UTC
I don't think it was Comcast specifically. I run my own DNS server and DNS resolution for all frontier sites starting failing. Something called "domainmonster" was returning bad A record results for frontier. Things were eventually fixed but I had to restart to clear cached results. I suspect Comcast had the bad records cached, possibly longer than they should have.