SUMMARY: TCP CLOSE_WAIT Adjustment, how?

From: Sawyer Curtis <SawyerCurt_at_bah.com>
Date: Fri, 14 Mar 1997 7:51

My original question was:

> I need to adjust the time that a TCP CLOSE_WAIT state will hang
> around. Under Solaris, I would use the following command to
reconfigure
> the time-out value to 1 minute:
>
> ndd -set /dev/tcp tcp_close_wait_interval 60000
>
> How would I do this under Digital UNIX 3.2c? (Before you tell me to
> RTFM, I am 7 miles from the building with the system and its
> documentation, and I do not have quick access to an X terminal with
which
> to read man pages.)

My thanks to all the help provided by Dejan Muhamedagic.

The answer, as provided by Dejan and quoted below, appears to be:

According to books, there are two timers concerning closing the
connection. One is 2MSL (2 mean segment life) used after the connection
is closed and FIN_WAIT_2 (tcp_maxidle) timer used if final FIN segment
does not arrive. The first one is usually set to 60 secs and for that
time a socket pair cannot be used for the next connection. However,
socket on your side can be reused if SO_REUSEADDR socket option is set.

... According to a TCP state transition
diagram, the CLOSE_WAIT state is the one server is found in after
receiving FIN segment from the client. Then, the server should send FIN
too and close the connection. The application controlling the connection
at the server side should issue a close system call. ...

RFC states that the connections should remain in CLOSE_WAIT and
FIN_WAIT2 states forever, but this is violated in most implementations.
This situation is also known as "tcp half-close", i.e. only one side has
closed the connection but data can still flow in the other direction.

The fix is:

It seems that you'll have to use dbx to change these params. Like this:
  cat <<EOF | dbx -k /vmunix
  assign tcp_msl = 60
  quit
  EOF
and you can put this into script to be called at startup.

Both tcp_msl and tcp_maxidle are set in units of 500ms and their default
values are 60 and 1200, respectively.

   Thanks again to Dejan Muhamedagic, whose responses are quoted
word-for-word above.
 ---Curt
 --
Curt Sawyer | sawyercurt_at_bah.com
      Booz Allen & Hamilton
       http://www.bah.com
Received on Fri Mar 14 1997 - 14:05:16 NZDT

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