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Date: Wed, 15 Jan 2014 12:15:48 +0100
From: Antonio Quartulli <antonio@meshcoding.com>
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Subject: Re: [B.A.T.M.A.N.] batman-adv 2014.0.0 released
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To: cmsv@wirelesspt.net, The list for a Better Approach To Mobile Ad-hoc Networking <b.a.t.m.a.n@lists.open-mesh.org>, =?UTF-8?B?TWFydGluIEh1bmRlYsO4bGw=?= <martin@hundeboll.net>

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On 15/01/14 12:13, cmsv wrote:
> inline:
>=20
> On 01/15/2014 02:00 AM, Martin Hundeb=C3=B8ll wrote:
>> Hi,
>>
>> On 2014-01-14 23:04, cmsv wrote:
>>> batman_adv: bat0: The MTU of interface adhoc0 is too small (1528) to
>>> handle the transport of batman-adv packets. Packets going over this
>>> interface will be fragmented on layer2 which could impact the
>>> performance. Setting the MTU to 1546 would solve the problem.
>>
>> Did you enable network coding? That would explain the message, as NC
>> uses a larger header to make decoding possible at the receiver side.
> Yes it is enabled by default as it was with batavd 2013.4.0 with 1528 m=
tu
>>
>> As far as I can tell from a quick look in packet.h, the required MTU
>> should be 1532 now. (10 bytes unicast + 8 bytes extra for unicast_4add=
r
>> + 14 ethernet =3D 32 bytes). Or am I bad at counting bytes?
>=20
> Regardless of being properly counted or not; dmesg outputs the message
> complaining about the need to make mtu 1546.

If you disable network coding the message will change.

The overhead is dynamic depending on NC being enabled or not and now the
message in dmesg tells you exactly what MTU you need.

Cheers,


--=20
Antonio Quartulli


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