[B.A.T.M.A.N.] batman-adv: is it possible to increase mtu size for batman-adv interfaces?

[B.A.T.M.A.N.] batman-adv: is it possible to increase mtu size for batman-adv interfaces?

[Andreas Pape]

Hi,

currently the mtu size of batman-adv soft-interfaces is limited to
ETH_DATA_LEN (1500 bytes) in function batadv_hardif_min_mtu as far as I
understand.

A comment in this function states that batman-adv "does not support MTUs
bigger than ETH_DATA_LEN". Is there a specific reason for this or would it
be possible to increase the MTU size to something like 1518 by simply
replacing all limitations to ETH_DATA_LEN with a higher value?

Kind regards,
Andreas



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Re: [B.A.T.M.A.N.] batman-adv: is it possible to increase mtu size for batman-adv interfaces?

[Sven Eckelmann]

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On Dienstag, 20. Juni 2017 07:49:28 CEST Andreas Pape wrote:
> Hi,
> 
> currently the mtu size of batman-adv soft-interfaces is limited to
> ETH_DATA_LEN (1500 bytes) in function batadv_hardif_min_mtu as far as I
> understand.
> 
> A comment in this function states that batman-adv "does not support MTUs
> bigger than ETH_DATA_LEN". Is there a specific reason for this or would it
> be possible to increase the MTU size to something like 1518 by simply
> replacing all limitations to ETH_DATA_LEN with a higher value?

There is no protocol specific reason why it is limited to 1500 bytes. But I 
think there is more needed than just changing all appearances of ETH_DATA_LEN. 
For example, at the moment we don't use more than 1500 and thus we didn't had 
to overwrite some of the special netdev variables for the maximum mtu. Maybe 
someone remebers the patches which wanted to touch this part of batman-adv but 
which were then dropped because batman-adv was only using an MTU of 1500 or 
less. Here is the revert of the change which tried that: https://
patchwork.kernel.org/patch/9390379/

There is most likely a lot more which will cause some kind of problem.

Kind regards,
	Sven

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