netdev - Re: [PATCH v3] ipv6: Limit mtu to 65575 bytes

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Message-ID: <20140411132207.GO27255@order.stressinduktion.org>
Date:	Fri, 11 Apr 2014 15:22:07 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	David Miller <davem@...emloft.net>,
	Francois WELLENREITER <f.wellenreiter@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH v3] ipv6: Limit mtu to 65575 bytes

On Thu, Apr 10, 2014 at 09:23:36PM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Francois reported that setting big mtu on loopback device could prevent
> tcp sessions making progress.
> 
> We do not support (yet ?) IPv6 Jumbograms and cook corrupted packets.
> 
> We must limit the IPv6 MTU to (65535 + 40) bytes in theory.
> 
> Tested:
> 
> ifconfig lo mtu 70000
> netperf -H ::1
> 
> Before patch : Throughput :   0.05 Mbits
> 
> After patch : Throughput : 35484 Mbits
> 
> Reported-by: Francois WELLENREITER <f.wellenreiter@...il.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> ---
> v3: fix title... humpff...

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Eric, the optimization for limiting the mtu in tcp case is still possible.
It is not that people don't care. ;)

Thanks,

  Hannes

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