How to listen or telnet between 2 ubuntu PCs, to verify firewall in ubuntu pc?

one way is to use telnet in a ubuntu pc

telnet <IP address> <Port>

telnet 44.55.66.77 9090

another way is to use nc for listening to a port

in the host pc: nc -l 9090

in the remote pc: nc 44.55.66.77 9090

then, type anything on remote pc, you should see it in host pc

If you want to check it from windows, open PowerShell:-

Test-NetConnection -ComputerName host -Port port

Test-NetConnection -ComputerName 192.168.0.1 -Port 80