netdev - Re: [PATCH] vxlan: Fix error that was resulting in VXLAN MTU size being 10 bytes too large

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Date:	Mon, 19 Nov 2012 22:33:50 +1100
From:	Joseph Glanville <joseph.glanville@...onvm.com.au>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, alexander.h.duyck@...el.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] vxlan: Fix error that was resulting in VXLAN MTU size
 being 10 bytes too large

On 14 November 2012 08:33, Stephen Hemminger <shemminger@...tta.com> wrote:
> On Tue, 13 Nov 2012 14:37:19 -0500 (EST)
> David Miller <davem@...emloft.net> wrote:
>
>> From: Alexander Duyck <alexander.h.duyck@...el.com>
>> Date: Fri, 09 Nov 2012 15:35:24 -0800
>>
>> > This change fixes an issue I found where VXLAN frames were fragmented when
>> > they were up to the VXLAN MTU size.  I root caused the issue to the fact that
>> > the headroom was 4 + 20 + 8 + 8.  This math doesn't appear to be correct
>> > because we are not inserting a VLAN header, but instead a 2nd Ethernet header.
>> > As such the math for the overhead should be 20 + 8 + 8 + 14 to account for the
>> > extra headers that are inserted for VXLAN.
>> >
>> > Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
>>
>> Applied, thanks for the detailed commit message.
>
> Probably need smarter code there to look at header length requirement
> of underlying device as well, maybe someone will be perverse and runn
> vxlan over a tunnel or IPoIB.

Forgive my ignorance but why would running VXLAN on IPoIB require
special header handling? (and would it work or behave strangely?)

I was planning on giving this a go when 3.7 is released but I might do
that sooner if problems are anticipated.

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Joseph.

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