netdev - Re: [PATCH] ipv6: Limit mtu to 65572 bytes

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Message-ID: <20140411025707.GM27255@order.stressinduktion.org>
Date:	Fri, 11 Apr 2014 04:57:07 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	Francois WELLENREITER <f.wellenreiter@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: Limit mtu to 65572 bytes

On Fri, Apr 11, 2014 at 11:30:44AM +0900, YOSHIFUJI Hideaki wrote:
> Eric Dumazet wrote:
> 
> > We must limit the IPv6 MTU to (65535 + 40) bytes in theory.
> > 
> > In practice, its better to align to a multiple of 4 for optimal TCP
> > performance.
> 
> It is a TCP issue.  We should not limit the mtu to 65532+40.
> I am for 65535+40. Otherwise, other protocol such as UDP cannot
> use full mtu as before.

I have not seen problems with max ipv6 mtu limit of 65535+40 and tcp.

I agree this would be a better approach, and maybe & ~3 the mtu/mss
in tcp code? I assume people expect maximum udp packet sizes working
over loopback?

Greetings,

  Hannes

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