Okay, so I'm pretty sure i have this right because i have tried a bunch of fixes over the past few days to get to this conclusion.
I think my IP address is for some reason being denied access to Apple servers.
I am able to sign into iCloud via my cellular connection.
But the moment I try to access or login to any of iCloud login (on mac/phone/windows pc) via my wifi (static IP) apple cannot sign me in and returns the error "unable to connect to server" or similar ones.
Does anyone know how to resolve this?
NB: I have done everything from router reset to fresh install of OS. in fact, when I was doing the install, I had to switch between mobile hotspot and wifi to ensure Apple verified my credentials and let me begin the install in the first place. Because over wifi, I couldn't even get El Capitan to download.
Best Answer
I think you may need to investigate your firewall settings on your router, or ask your ISP if they know of any particular ports that may be blocked & how to change that.
The list of ports & services required for all software Apple access is fairly substantial, but is all detailed at Apple's Knowledge Base: TCP and UDP ports used by Apple software products