Also, if you are trying to connect to a resource from a restrictive network your knocking sequence might be blocked by filters at the client end. I've been on

Also, if you are trying to connect to a resource from a restrictive network your knocking sequence might be blocked by filters at the client end. I've been on networks that allow nothing except the standard TCP & UDP ports for HTTP(S), SSH and DNS (and even then DNS was restricted to their local name server).