how to check if port is open - ilya-khadykin/notes-outdated GitHub Wiki
Using telnet to check if a port is open on a remote host
A common problem in a WAN environment is that a firewall or other network filter prevents connectivity with this port. You can run a simple troubleshooting test to make sure the Client can connect to the port. Just try to telnet (over TCP) to the port from the Client.
This is how to check if a port is open on a remote host in Windows:
Telnet tserv 3389
# tserv - host name
# 3389 - port number
If telnet is successful, you simply receive the telnet screen and a cursor. This test tells you that you can connect over the port