netdev - Re: [RFC] tcp: allow timestamps even if SYN packet has tsval=0

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Message-ID: <Pine.LNX.4.64.0903120858550.4697@wrl-59.cs.helsinki.fi>
Date:	Thu, 12 Mar 2009 09:26:20 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	dada1@...mosbay.com, Netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] tcp: allow timestamps even if SYN packet has tsval=0

On Wed, 11 Mar 2009, David Miller wrote:

> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Wed, 11 Mar 2009 13:17:54 +0100
> 
> > So apparently WindowsXP sends a NULL tsval in SYN packet, then
> > subsequent packets get a real value (60498) in this case.
> > 
> > This seems to work on other OS as well, so is the following patch
> > considered evil ?  Do we have security concerns or only risking
> > windows client to have slightly wrong rtt estimation at the begining
> > of the tcp session ?
> 
> I think we'll have to accept this.
> 
> I don't see other systems blocking initial ts_ecn values of
> zero like we do.

What about the fact that PAWS could bite us leaving us a hung connection 
if timestamp changes too much when we get the first ACK? Though I doubt 
you can get windows to run long enough for this to become a problem if 
they always start from zero... ;-)

-- 
 i.
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