We have been having an issue with our ISP (Roger's) shutting down our internet service for what they are saying is an "Open DNS" on our system. This is a new one. There's never been a problem before and the system has been in place for years. We have Trend-Micro Worry Free Business and I have tried blocking port 53 for inbound, BUT, of course, then all client computers on the network cannot access the internet. Also, it will interfere with Exchange access. We have one server and a static IP service.
What I've tried:
- Turned off Recursion: clients could no longer access web sites
- Blocked port 53 (Inbound) - In Trend Micro Firewall: clients couldn't access web sites
- Blocked Port 53 (outbound) - In Trend Micro Firewall: Did not resolve security issue
*** Rgers gave us a web site to check the open DNS: www.thinkbroadband.com/tools/dnscheck.html
When port 53 is blocked in the Trend Micro this web check shows the DNS issue as resolved, however, when not blocked it shows a problem.
How can I resolve this issue and still allow clients to access the internet web pages?