Status of TCP connections
The status of a TCP connection can be one of the following:
The TCP connection has been accepted by the remote party and is still active.
The TCP connection has been closed after being successfully established.
The remote party acknowledged the initial SYN message by a RST message; i.e. the remote party does exist, but no service is bound to the request port. Note: Most personal computers are protected by a firewall that discards RST messages to prevent effective port scanning.
The remote party does not acknowledge the SYN message; i.e. the remote party does not exist or it is protected by a firewall.
The TCP connection was rejected by the operating system itself; for instance due to security settings.