Our IT Network staff recently did a network upgrade for a new customer who was getting a new ISP, and when we finished the customer couldn’t get to their website. Seems like a DNS issue, but it wasn’t. We could use just the Comcast router and go to the website, but when we added our Firewall with no rules set the site was blocked.
The issue turned out to be a Security feature in the Comcast router. A featured called “Securityedge”. Once we determined it could be this feature we were unable to turn it off via the router. The only way to turn off this feature was to ask Comcast to turn it off.
Let us know if this helped you….