1. Open up a terminal shell.
2. Type

netstat -an

-a - this parameter defines that you want to view all connections
-n - this parameter defines that you wish to view the address of the remotely connected server/user in numerical format rather than by hostname.


Additional useful parameters:

-p - this will print the name of the executable file that is in communication with the remote client
-v - When used in conjunction with -b, will display sequence of components involved in creating the connection or listening port for all executables.