Thanks for the answer. After analyzing the packets of the communications between my network and the domain Github.com. I became with the conclusion that Github servers were blocking us since the signal returned was hello and then reset packets.
I “found” the problem, as you correctly said, one of the corporate proxies were blocking the communication. When I was trying to bypass the proxy, I had to put it back because one of the patch cords were too short, so, I couldn’t bypass it. Immediately, everything started to work.
So, I don’t know yet what was the problem. It will require a little more of troubleshooting.