Re: [B.A.T.M.A.N.] [PATCH maint] batman-adv: fix soft-interface MTU computation

Antonio Quartulli
2014-01-22T07:03:07Z

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On 22/01/14 07:04, Russell Senior wrote:
>>>>>> "Russell" == Russell Senior <russell@personaltelco.net> writes:
>
>>>>>> "Antonio" == Antonio Quartulli <antonio@meshcoding.com> writes:
> Antonio> The current MTU computation always returns a value smaller
> Antonio> than 1500bytes even if the real interfaces have an MTU large
> Antonio> enough to compensate the batman-adv overhead.
>
> Antonio> Fix the computation by properly returning the highest
> Antonio> admitted value.
>
> Antonio> Signed-off-by: Antonio Quartulli <antonio@meshcoding.com> ---
>
> Russell> This seems to fix the bat0-MTU-unnecessarily-small problem I
> Russell> observed last night and reported on the IRC channel. I
> Russell> haven't actually passed any traffic over it yet, but the
> Russell> interface is up with the expected MTU value with the patch.
>
> Antonio> This patch is missing a Reported-by clause because I did not
> Antonio> have "russell"'s email address at hand.
>
> Russell> Reported-by: Russell Senior <russell@personaltelco.net>
>
> Followup, as requested, I tried setting a smaller MTU (1400) on the
> adhoc0 interface. When fragmentation was enabled, this resulted in no
> change to MTU (still 1500) for bat0. When I disabled fragmentation,
> the bat0 MTU dropped, as expected, to 1368. Interestingly, the MTU on
> the bridge that bat0 was a member of remained 1500 despite the lower
> bat0 MTU. Should that be?
>

I don't really know how the bridge code behaves. As far as I remember it
should adapt to the smallest MTU.

But thanks for testing! This shows that the patch is working fine ;)

--
Antonio Quartulli

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