TCP States
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TCP States

An explanation of common TCP states.


SYN_SEND Indicates active open.

SYN_RECEIVED Server just received SYN from the client.

ESTABLISHED Client received server's SYN and session is established.

LISTEN Server is ready to accept connection.

NOTE: See documentation for listen() socket call. TCP sockets in listening state are not shown - this is a limitation of NETSTAT. For additional information, please see the following article in the Microsoft Knowledge Base:

134404 NETSTAT.EXE Does Not Show TCP Listen Sockets

FIN_WAIT_1 Indicates active close.

TIMED_WAIT Client enters this state after active close.

CLOSE_WAIT Indicates passive close. Server just received first FIN from a client.

FIN_WAIT_2 Client just received acknowledgment of its first FIN from the server.

LAST_ACK Server is in this state when it sends its own FIN.

CLOSED Server received ACK from client and connection is closed.

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