netstat : check open ports and connections to system

Using netstat command we can see all the used and listening ports on your computer. NETSTAT command will work in Windows and as well as in Linux Operating System.
Linux
Will Show all connected Ports
netstat -an | grep -i "connected"

Will Show all listening Ports
netstat -an | grep -i "listening"

Will Show all established connections
netstat -an | grep -i "established"

Windows 
Will Show all connected Connected Ports
netstat -an |find /i "connected"

Will Show all listening Ports
netstat -an |find /i "listening"

Will Show all established connections
netstat -an |find /i "established"

Note: -i & /i is used to ignore case-sensitive.