TCP/IP State Transition Diagram (RFC793)
Gordon McKinney (23 Feb 2002)
A connection progresses through a series of states during its lifetime. The states are: LISTEN, SYN-SENT, SYN-
RECEIVED, ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT, and
the fictional state CLOSED. CLOSED is fictional because it represents the state when there is no TCB, and
therefore, no connection. Briefly the meanings of the states are:
LISTEN represents waiting for a connection request from any remote TCP and port.
SYN-SENT represents waiting for a matching connection request after having sent a connection request.
SYN-RECEIVED represents waiting for a confirming connection request acknowledgment after having both
received and sent a connection request.
ESTABLISHED represents an open connection, data received can be delivered to the user. The normal state
for the data transfer phase of the connection.
FIN-WAIT-1 represents waiting for a connection termination request from the remote TCP, or an
acknowledgment of the connection termination request previously sent.
FIN-WAIT-2 represents waiting for a connection termination request from the remote TCP.
CLOSE-WAIT represents waiting for a connection termination request from the local user.
CLOSING represents waiting for a connection termination request acknowledgment from the remote
LAST-ACK represents waiting for an acknowledgment of the connection termination request previously
sent to the remote TCP (which includes an acknowledgment of its connection termination
TIME-WAIT represents waiting for enough time to pass to be sure the remote TCP received the
acknowledgment of its connection termination request.
CLOSED represents no connection state at all.
A TCP connection progresses from one state to another in response to events. The events are the user calls,
OPEN, SEND, RECEIVE, CLOSE, ABORT, and STATUS; the incoming segments, particularly those containing
the SYN, ACK, RST and FIN flags; and timeouts.