How to knock on a machine with an internal IP through an external IP?

Question

linux

I have 2 cars. 1 with external IP another in the internal network. I need to be able to walk to a machine on the internal network from outside. I'd like to organize this through a machine that has an external IP. Frankly, I haven’t been involved in networks for a long time and I don’t want to spend a lot of time searching. this moment is only a means, not the end of the work. Please let me know where I can read more about this. (both machines on CentOS)

Answer 1

the easiest way is to forward the port to the machine on the internal
network
where
EXT_R_IP - external ip
PORT1 - external port for connecting via ssh (for example 5810)
LOCAL_IP - ip of the machine on the local network to which you need to forward the port
PORT2 - local ssh port, standard 22
If the network raises the router, then everything is intuitively clear
wiki
opennet
google

Answer 2

Either on the proxy through which the machine from the internal network goes to the external one, hardcode the port to communicate specifically with this machine, or install software on the machine on the internal network that will itself constantly knock on the external server and use it to establish a connection.
teamviewer usually solves common problems with accessing machines behind a proxy server.