Telnet
From Dikapedia
telnet -- user interface to the TELNET protocol. Useful to do a quick connection test to a remote server on a specific port.
(Nmap might be more useful at times)
How to use Telnet
To test is port 22 (SSH) is open on a remote server:
$ telnet 34.195.120.102 22 Trying 34.195.120.102... Connected to 34.195.120.102. Escape character is '^]'. SSH-2.0-OpenSSH_7.4
To escape, hit ctrl + ].
You will get dropped down to the telnet prompt. To quit, hit q then enter.
$ telnet 34.195.120.102 22 Trying 34.195.120.102... Connected to 34.195.120.102. Escape character is '^]'. SSH-2.0-OpenSSH_7.4 ^] telnet> q Connection closed.
How to open a listener for Telnet
If you simply just want to test connectivity but don't have a process listening on a particular port, you can simply open a listener using nc -l command:
1) On listening host run the following to open a listener on port 1500:
nc -l 1500
2)On the client machine, run the following command to check connectivity:
telnet <ip> 1500
How to telnet from a Windows machine
PS C:\windows\system32> test-NetConnection 172.18.12.43 -port 22 ComputerName : 172.18.12.43 RemoteAddress : 172.18.12.43 RemotePort : 22 InterfaceAlias : Ethernet 3 SourceAddress : 172.24.113.86 TcpTestSucceeded : True