netdev - Re: Bad TCP timestamps on non-PC platforms

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Message-ID: <1294366281.2704.36.camel@edumazet-laptop>
Date:	Fri, 07 Jan 2011 03:11:21 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alex Dubov <oakad@...oo.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: Bad TCP timestamps on non-PC platforms

Le jeudi 06 janvier 2011 à 17:55 -0800, Alex Dubov a écrit :
> Sorry for the awful synopsis of my problem. I never cease to amaze myself
> at how bad those usually turn up. :-)
> 
> What I really meant to write is:
> 
> I have a dev board running 2.6.37-rc7. Normal kernel config, nothing fancy.
> Remote machines are just usual linux boxes in constant operation (I tried
> several of those).
> 
> UDP/DHCP works correctly all the time, so ethernet side is probably ok.
> 
> When tcp_timestamps are enabled, SYN packets from dev board just get
> ignored by the remote side. I see them arrive in wireshark, but nothing
> else happens.
> 
> When I disable tcp_timestamps on the dev board everything works.
> 
> The problem is reproducible every single time.
> 
> The only difference is the "Options" block of the SYN packets.
> If timestamps are not really to blame, then it probably window scale
> parameters. That's what I see on a usual dropped packet:
> 
> Options: (20 bytes)
>         Maximum segment size: 1460 bytes
>         SACK permitted
>         Timestamps: TSval 4294893842, TSecr 0
>         NOP
>         Window scale: 5 (multiply by 32)
> 
> 
> 
>       


You dont give new informations ;)

I asked if you could give information on the other side : The bug is to
drop this legal packet.

uname -a
sysctl -a | grep tcp


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