I have issues when accessing port 80 from an internal network.
On the router I have the below set up:
NAT, Open Ports, WAN IP is set and Local computer IP is set.
TCP Start port 80 end port 80.
This was set up for a CRM, within this CRM you can send posts via outlook that contain an external web address, this web address uses port 80 to access a server. You get a prompt to login, once typed in username and password takes you straight through.
When clicking on this link internally, you are going outside of network and then coming back in again. This is where a login problem occurs and you are denied entry, however it is intermittent and sometimes works and sometimes doesn’t.