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From: David Miller <davem@davemloft.net>
Subject: Re: [RFC] tcp: allow timestamps even if SYN packet has tsval=0
Date: Wed, 11 Mar 2009 09:24:25 -0700 (PDT)
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From: Eric Dumazet <dada1@cosmosbay.com>
Date: Wed, 11 Mar 2009 16:00:02 +0100

> [PATCH] tcp: allow timestamps even if SYN packet has tsval=0
> 
> Some systems send SYN packets with apparently wrong RFC1323 timestamp
> option values [timestamp tsval=0 tsecr=0].
> It might be for security reasons (http://www.secuobs.com/plugs/25220.shtml )
> 
> Linux TCP stack ignores this option and sends back a SYN+ACK packet
> without timestamp option, thus many TCP flows cannot use timestamps
> and lose some benefit of RFC1323.
> 
> Other operating systems seem to not care about initial tsval value, and let
> tcp flows to negotiate timestamp option.
> 
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

And amusingly even Linux didn't care for ipv6 TCP sockets ;-)

Applied to net-next-2.6, thanks Eric.