Status of TCP connections

The status of a TCP connection can be one of the following:

established

The TCP connection has been accepted by the remote party and is still active.

closed

The TCP connection has been closed after being successfully established.

no service

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.

no host

The remote party does not acknowledge the SYN message; i.e. the remote party does not exist or it is protected by a firewall.

rejected

The TCP connection was rejected by the operating system itself; for instance due to security settings.