I had the following issue with my installation of ISPConfig 3.1 (recently upgraded): When attempting to login, by entering the host name on the address bar, (ie. https://vps.mydomain.com:8080), login gets stuck in a loop, continuously reloading the login screen, even though the password is correct. However, if I reach the admin site by IP address such as https://10.10.10.126:8080, the login works fine. I did 2 upgrades on 2 different machines, with the exact same result. Then, I thought it was because of the upgrade, so I created a brand new installation, using the tutorial here , and the result was exactly the same. Anyone have any ideas what may be going on here? Best regards.