How to set up a router for only one site?

Question

network hardware

In short, the story is this.: When I served in the army, I was a signalman. And in our communication center there was a computer with a special Internet network, which for some reason everyone called VPN , although it was a completely different thing.
This was like some kind of chat only between military units. To access it, you had to write a specific IP address in the domain input line, this computer did not go to other sites. Well, we had one single sergeant there who was messing around with DNS and with the Router settings that could go to any sites, but this creature did not tell how he does it. Even the head of communications did not know how to access other sites. That sergeant studied to be a programmer and therefore knew how it works. It was even impossible to go into the router settings there, but the boys and I dug intoDNS settings and made it so that it was still possible to go into the router settings, but at the same time that site stopped working because the IP of this site was written in DNS and we changed it to IP from the router. So the question is how did they make it possible to go only to this site and not to others? And what else did that sergeant do such that the usual network either opened or closed?

Answer 1

registered / removed DNS