netdev - Re: TCP connection will hang in FIN_WAIT1 after closing if zero window is advertised

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Message-ID: <541802EC.1060308@oktetlabs.ru>
Date:	Tue, 16 Sep 2014 13:29:16 +0400
From:	Andrey Dmitrov <andrey.dmitrov@...etlabs.ru>
To:	Neal Cardwell <ncardwell@...gle.com>
CC:	Netdev <netdev@...r.kernel.org>,
	"Alexandra N. Kossovsky" <Alexandra.Kossovsky@...etlabs.ru>,
	Konstantin Ushakov <kostik@...etlabs.ru>
Subject: Re: TCP connection will hang in FIN_WAIT1 after closing if zero window
 is advertised

On 15/09/14 23:43, Neal Cardwell wrote:
> On Mon, Sep 15, 2014 at 12:11 PM, Andrey Dmitrov
> <andrey.dmitrov@...etlabs.ru> wrote:
>> It is possible to create a lot of connections in the same manner which will be in FIN_WAIT1 state forever.
> ...
>> After ~10 minutes you will see 500 connections in the FIN_WAIT1 state on the host_A:
>> netstat | grep FIN_WAIT1 | wc -l
>> 500
> Thanks for the report. In your tests, have you ever seen the number of
> such connections exceed net.ipv4.tcp_max_orphans?
>
> Can you set net.ipv4.tcp_max_orphans to a low value and verify that it
> limits the number of such connections? AFAICT it should.
I tried to set net.ipv4.tcp_max_orphans to 100, it limits the 
connections number. As I saw net.ipv4.tcp_max_orphans can be exceeded, 
but for a short time. Maximum connections number in FIN_WAIT1 state was 
196, after that it was decreased rather fast to ~100.

Thanks,
Andrey
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