netdev - Re: [RFC] IP_MAX

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Date:	Fri, 21 Dec 2012 10:54:05 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] IP_MAX_MTU value

On Fri, 2012-12-21 at 10:50 -0800, Rick Jones wrote:
> On 12/21/2012 10:34 AM, Eric Dumazet wrote:
> > On Fri, 2012-12-21 at 10:19 -0800, Rick Jones wrote:
> >
> >> If you go beyond the protocol limit of an IPv4 datagram, won't it be
> >> necessary to  start being a bit more conditional on IPv4 vs IPv6?
> >>
> >
> > This IP_MAX_MTU is really an IPv4 thing (static to net/ipv4/route.c)
> 
> OK. Doesn't this:
> 
>          if (mtu > IP_MAX_MTU)
>                  mtu = IP_MAX_MTU;
> 
> mean it should be OK to go to 0xFFFF but not 0x10000?  Since 65535 is 
> the limit of an IPv4 datagram and so I would think would be the maximum 
> MTU for an IPv4 interface.

Sure, I meant 0xFFFF and it is the value I used in my tests.

65536 is the current MTU of loopback device, and this can be used by
other protocols.



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