linux-kernel - Re: tcp_tw

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Message-ID: <20081115155228.GZ24654@1wt.eu>
Date:	Sat, 15 Nov 2008 16:52:28 +0100
From:	Willy Tarreau <w@....eu>
To:	Karl Pickett <karl.pickett@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: tcp_tw_recycle broken?

On Sat, Nov 15, 2008 at 10:47:10AM -0500, Karl Pickett wrote:
> On Sat, Nov 15, 2008 at 8:09 AM, Andi Kleen <andi@...stfloor.org> wrote:
> > "Karl Pickett" <karl.pickett@...il.com> writes:
> >>
> >> May I just confirm.. is tcp_tw_reuse NOT dependent on receiving timestamps?
> >
> > The big problem is that both are incompatible with NAT. So if you
> > ever talk to any NATed clients don't use it.
> >
> > -Andi
> >
> > --
> > ak@...ux.intel.com
> >
> 
> 
> Hmph.  Running the test again - after getting a little sleep -
> timestamps do indeed determine if tw_reuse/recyle work.  I must not
> have let all the tw buckets expire before changing my timestamp
> settings last night.
> 
> Since
> A. I don't want to rely on arbitrary web servers having timestamps
> B. People say it breaks NAT for clients, and the settings are global only,
> 
> I will just set TCP_TIMEWAIT_LEN to 10 seconds and call it a day.

you should increase it a bit. I've encountered occasional issues at 15s,
but none at 20s.

> Sure would be nice if it was a tunable, so only the most heavily
> loaded customers could set it...

Indeed. other OSes (eg Solaris) ship with standard values and let us adjust
them.

Willy

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