On Thu, Dec 13, 2007 at 02:25:21AM -0500, Daniel Ouellet wrote:
> Otto Moerbeek wrote:
>> I'm only talking about the tear-down. The three-way handshake happens
>> before that, both sockets are in ESTABSLIHED state. You have to read
>> half-close as a verb (action), and half-open as a description of the
>> state of the connection. Check the state transition diagram, and maybe do
>> some reading in
>> Stevens's TCP/Illustrated Volume I (which has the state diagram on the
>> inside cover ;-)
>
> I did a lots of reading and I cleared my miss understanding looks like and
> see where I confuse myself:
>
> 1) A socket gets into CLOSE_WAIT when the remote side sends a FIN and the
> local side sends an ACK, but has not yet sent it's FIN.
>
> 2) A socket gets into FIN_WAIT_2 when the local side closes the socket and
> sends a FIN (FIN_WAIT_1) and then receives an ACK for that FIN but has not
> yet received a FIN from the remote side.
>
> I got confuse as I can't never see any CLOSE_WAIT on my server, no complain
> for sure but I see a FIN_WAIT_2 and obviously confuse the two.
>
> I am puzzled as to why they would get so many CLOSE_WAIT and I guess it
> might be an under power server may be that when the httpd child process is
> done, that the master, or what not don't have time to process it and as
> such keep the socket open because of that. Not sure, but I guess possible.
>
> In any case, I appreciate the reply and I sure clear that part of the
> handshake anyway, so I will not make the same mistakes again. (;>
>
> Best,
>
> Daniel
It's easy to force a socket into CLOSE_WAIT
On server:
$ nc -l 10000
On client:
$ nc 10000
That gets you ESTABLISHED on both sides.
^Z the server side
close the client side by typing ^D
The client moves to FIN_WAIT_2, and the server to CLOSE_WAIT.
fg the server process
The client moves to TIME_WAIT and the server socket will disappear.
It's depening on the application if sockets staying in CLOSE_WAIT are
a problem or not: it might be intentional (in the hulp duplex case),
or it might be a program "forgetting" to do a close.
-Otto
BTW: it's volume II that has the state diagram on the inside cover.
Volume I has it in chapter 18, after the discussion of half-close.
