# nc -z -v [hostname or IP address] [port number]
nc -z -v 192.168.100.1 443
Connection to 192.168.100.1 443 port [tcp/https] succeeded!
# nc -z -v -u [hostname or IP address] [port number]
# nc -z -v -u 192.168.100.1 123
Connection to 192.168.100.1 123 port [udp/ntp] succeeded!
We can also test TCP port with telnet command
telnet [hostname or IP address] [port number]
# telnet 192.168.100.1 443
Connected to 192.168.100.1.
Escape character is '^]'.
If return “Connected to xxx.xxx.xxx.xxx”, it means the port is open and functional
If return “Trying xxx.xxx.xxx.xxx…”, it means the port is closed or not accessible.
Keywords: Internet connection, Limited internet access, netsh, winsock, ipconfig, Microsoft Windows, WiFi, WiFi Router, Modem
Sometimes, you will find that your computer can only access Google, or microsoft.com etc.
For Mirosoft Windows there are many tricks you can try:
1 Win + R
2 Type cmd and hit Enter key.
Try each of these and hit enter at the end of each line
(If use netsh int ip reset, ignore netsh int ipv4 reset and netsh int ipv6 reset)
netsh winsock reset
netsh int ip reset
netsh int ipv4 reset
netsh int ipv6 reset
3 Restart your computer
4 Follow step 1-3 and type following commands, hit enter at the end of each line
5 Wait 3 minutes
If you still can not get online.
Try to power cycle/restart your WiFi/Router/Modem. (Normally the box at home or small office you use to access WiFi and internet.)
A simple open source Windows utility software for testing/benchmark your network speed, very handy when you just want to quickly test your LAN speed between two computers.
(Also available as portable version)