View Source: TcpStates - Waikato Linux Users Group

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States of a [TCP] connection.  These can be seen with
 netstat -at

;CLOSED:A theoretical state where a [TCP] connection doesn't exist yet.
;LISTEN:A state where [TCP] connection is waiting for a connection to be made to it.
;SYN_RCVD: A [SYN] has been received, a SYN ACK has been sent, and we are waiting for an [ACK]
;SYN_SENT: A [SYN] has been sent to start a connection, the SYN ACK hasn't yet been received.
;ESTABLISHED: A connection has been established
;CLOSE_WAIT:After a [TCP] connection has been closed, the spec says you should make sure that the connection is not reopened for a few minutes to prevent packets that were delayed in the Internet causing the connection to be reopened.  These will disappear by themselves after a while.  This can cause problems on servers that have lots of very short connections (such as a web server) by filling up the OS's connection table. See also [EADDRINUSE]
;LAST_ACK:A [FIN] has been received, we've sent our own FIN, but we are waiting on the ACK before we can move to the closed state.
;FIN_WAIT_1:A FIN has been sent, waiting for a ACK or FIN
;FIN_WAIT_2:A FIN has been sent, and an ACK has been received.  More data can be received.  This connection is half open.
;CLOSING:A FIN has been sent, and one received, the FIN hasn't been ACK'd yet.
;TIME_WAIT:The connection has closed, and is waiting for 2MSL
----
The amount of time that a connection waits in various stages is controlled by the OperatingSystem. Some OS'es let you tune these settings. For example, for Linux-based OSes, look in /proc/sys/net/ipv4.

From /usr/src/linux/Documentation/filesystems/proc.txt:

tcp_syn_retries:
  Number of  times  initial  SYNs  for  a  TCP  connection  attempt  will  be retransmitted. Should  not  be  higher  than 255. This is only the timeout for outgoing connections,  for  incoming  connections the number of retransmits is defined by tcp_retries1.

tcp_fin_timeout:
  The length  of  time  in  seconds  it  takes to receive a final FIN before the
  socket is  always  closed.  This  is  strictly  a  violation  of  the  TCP
  specification, but required to prevent denial-of-service attacks.

tcp_retries1:
  Defines how  often  an  answer  to  a  TCP connection request is retransmitted
  before giving up.

tcp_retries2:
  Defines how often a TCP packet is retransmitted before giving up.
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Version 6, saved on Thursday, May 26, 2005 3:50:19 pm by DanielLawson
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