Debian server visibility outside of a remote desktop

I am working on a Debian system at a sister company, and have a VPN set up between the 2 sites. I am able to Remote Desktop onto any of their other servers, but no their Debian server. I am able to access the IP address for the Bebian system through a browser on any of their network boxes, but cannot access from outside.

The only way I'm able to access the Debian box is to RDP onto any other server within their system, and then RDP from there to the Debain system. Doing this way though prevents me from sending files as I am unale to SSh or PFTP to the Debian box form my VMWAre testing system's Command Terminal, which I have been using throughout previously.

In the past I found a command that was entered into the Debian terminal through RDP that opened up a port on the box, that since then enabled access, but following a recent server reboot, the connection has once again been lost.

Is there a command that will sort this problem, when entered into the Command Terminal of the debian box whilst RDP'd onto it?
Neil BrookesIT DeveloperAsked:
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nociSoftware EngineerCommented:
You probably did open up a port, but didn't save  the results.

If you use the command to open the port again and then use:
service iptables save

on more recent system YMMV, systemd introduces more issues how to filter and resolve... So more info is needed here on the setup of your debian box. (version, type of firewall used (iptables, or other).
Neil BrookesIT DeveloperAuthor Commented:
It seems iptables isn't present on the server, typing iptables brings back: bash: iptables: command not found, and trying sudo iptables returns: iptables v1.4.14: no command specified Try 'iptables -h' or 'iptables --help' for more information.
I can ip link and get a response, but unable to copy and past into here as the connection I have will not allow.
David FavorLinux/LXD/WordPress/Hosting SavantCommented:
If there's no iptables, there still may be some other firewall running.

Install iptables + try something like iptables -nL to dump all Kernel rules.

Or nft list ruleset if they're using NFT.
nociSoftware EngineerCommented:
iptables command would only run from the "root" commandline.

after sudo use:
iptables -nv -L
iptables-save   #to get it all (nat, mangle, filter)
Neil BrookesIT DeveloperAuthor Commented:
Problem found to be the server was listening on the wrong gateway. Have now corrected in the Debian terminal and this now allows access to the website held on the browser via a web browser as intended.

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