When I setup gitolite on my server for Git access through SSH, of course I did test that cloning worked from outside my network. That was for my Paperweb project.
Later I configured port-knocking on the server to get rid of bot-based authentication attempts that were polluting my log files. Unfortunately, at this time, the “outside” server on which I have an account was down, so I could not leave my network to check that all was fine; from the inside of the network, all worked like a charm, though!
Same situation when someone asked me for the Paperweb code by e-mail because they could not get it the normal Git way. I had no idea that port-knocking was the problem: from my side of the firewall, all worked correctly…