Why can't I connect to the remote server?

Question

Windows

There is a remote server on Linux with a database and 2 separate grids from which you need to connect to this server. On the server, dynamic DNS is connected, the port is forwarded, in general, everything is fine. The problem is different from the same grid, the computer on Windows 10 connects to the database without problems, everything works fine. And from the second grid, the client program does not want to connect to the database. Moreover, in both networks there is one provider, the same modems, identical settings and firmware on the modems. What could be the reason? I did not touch the Internet connection settings.

Answer 1

Check the availability of the port from the second network using telnet. If telnet fails, look at Linux IPtables and firewall settings of the remote network.

Answer 2

How is the client connected? By name or by IP?
What does ping a server say to an address from both networks?
If it doesn't ping what route says
Well, what does the firewall think on the server with the base for incoming connections on the right protocol to the right port from both networks.
tcpdump to the rescue!
Yes! And what does ip route think | sort on linux server side?