Ensure the stable connection between hardwares.(If the hardware connection is normal, the NIC should light on.) 2. Make sure the target IP is correct (the local IP is 127.X.X.X) by executing ping command. 3. Make sure the server port is the same as the client. Try to telnet the target port (Generally, if you can ping the target IP but cannot connect to the target port, it was mainly disable by the firewall or router).