"netstat -a" shows many connections with a status of FIN_WAIT_2

Technote (troubleshooting)


Problem(Abstract)

You are running the IBM® HTTP Server on AIX® and are noticing that when issuing a netstat -a that many connections have a status of FIN_WAIT_2. This symptom usually occurs on AIX platforms running high traffic web sites and does not indicate a problem with the IBM HTTP Server.

Cause

Some clients or browsers never properly close their side of the connection (possibly a bug in the browser, the clients TCP stack or perhaps the client is dialed in and the dial-up link drops before the shutdown completes).

There might be other causes, but these are the most common.


Resolving the problem

  • Impact:
    If too many FIN_WAIT_2 sessions build up, it can fill up the space allocated for storing connection information and crash the Kernel.

  • Resolution or workaround:
    The right way to handle this problem is for the TCP/IP stack to have a fin_wait2 timer that will shutdown sockets stuck in fin_wait2 state.

    By default, a socket in TIME_WAIT will be cleaned up in 600 seconds (tcp_keepintvl * tcp_keep_alive_retry):
    • tcp_keepintvl is tunable.
    • tcp_keep_alive_retry is not tunable (set to 8).
    • tcp_keepintvl defaults to '150' half second intervals (75 seconds). Times 8 is 600 seconds.
    • You can reduce this 600 second timeout by reducing tcp_keepintvl.
    • You should be able to set tcp_keepintvl to as low as 30 (from 150) which should cause the TIME_WAIT sockets to time out in 2 minutes (rather than 10 minutes).

  • How to set the value:
    1. Note what the current setting is by entering the following command (it should be 150):

      no -o tcp_keepintvl

    2. Login as root.

    3. To change the value, enter the following command:

      no -o tcp_keepintvl=30

  • Since AIX 4.3, FIN_WAIT2 can be controlled using the no command

Example:
To reduce fin_wait2 time out to one minute, the command is no -o tcp_finwait2=120

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Document information


More support for:

IBM HTTP Server

Software version:

6.0, 6.1, 7.0, 8.0, 8.5, 8.5.5

Operating system(s):

AIX

Reference #:

1008268

Modified date:

2013-09-10

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