Every now and again you need to troubleshoot firewall rules and Telnet is a great tool to help understand if a port is open or not between two devices.
However Telnet is not enabled by default anymore, it has been like that since Windows Server 2008.
The following Powershell commands will help you to quickly enable it:
Import-Module Servermanager Add-WindowsFeature Telnet-Client
Installing the Telnet client doesn't require a reboot.
The client can also be removed easily via Powershell with these commands:
Import-Module Servermanager Remove-WindowsFeature Telnet-Client