Try the door.
Mind the port.

Choose a door to knock on.

Replace HOST with your authorized hostname or IP address, and PORT with the service’s TCP port number.

nc -vz -w 5 HOST PORT

Netcat options differ between implementations; check nc -h locally. Timeout behavior can also vary, especially during name resolution.

Test-NetConnection -ComputerName HOST -Port PORT

In PowerShell, inspect TcpTestSucceeded. Other output may include a separate ping test; that is not the result of the TCP check.

A handshake is not a conversation.

A successful connection means the TCP endpoint accepted a handshake. It does not verify TLS, authentication, or application health. Follow up with an HTTPS check if you are investigating a web service.

Refused, or simply unanswered?

A refusal generally means an active rejection from the destination or an intervening device. A timeout may mean filtering, a routing problem, or an unresponsive host. Neither result, alone, explains the whole network.