Netstat

About
Netstat (NETwork STATistics) is a command line tool that provides network information about your activity. If used on a local computer, netstat will display all activity for that one machine, however; if its a network server then netstat will display all activity for all machines connected onto the network.


 * Protocol: whatever protocol is being used. Its either TCP which is connection oriented and once a connection is established, data can be sent bidirectional. UDP is a simpler, connection-less Internet protocol. Multiple messages are sent as packets in chunks using UDP.
 * Local Address: is the local host machine name or host IP and port number
 * Foreign Address: is the remote machine name or remote IP and the port number
 * State: either established (meaning currently transmitting data) or time_wait (meaning a connection was made but not currently transmitting)

Simply open a command shell and type netstat -an.

Socket States
The possible socket states are as follows:


 * ESTABLISHED: The socket has an established connection.
 * SYN_SENT: The socket is actively attempting to establish a connection.
 * SYN_RECV: A connection request has been received from the network.
 * FIN_WAIT1: The socket is closed, and the connection is shutting down.
 * FIN_WAIT2: Connection is closed, and the socket is waiting for a shutdown from the remote end.
 * TIME_WAIT: The socket is waiting after close to handle packets still in the network.
 * CLOSED: The socket is not being used.
 * CLOSE_WAIT: The remote end has shut down, and the socket is closed.
 * LAST_ACK: Waiting for acknowledgement.
 * LISTEN:The socket is listening for incoming connections. Such sockets are not included in the output unless you specify the --listening (-l) or --all (-a) option.
 * CLOSING: Both sockets are shut down but we still don't have all our data sent.
 * UNKNOWN: The state of the socket is unknown.