netdev - Re: [PATCH net-next v4] ip6_vti: adjust vti mtu according to mtu of lower device

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Date:   Wed, 20 Dec 2017 11:53:08 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     alexey.kodanev@...cle.com
Cc:     netdev@...r.kernel.org, steffen.klassert@...unet.com,
        pvorel@...e.cz, shannon.nelson@...cle.com
Subject: Re: [PATCH net-next v4] ip6_vti: adjust vti mtu according to mtu
 of lower device

From: Alexey Kodanev <alexey.kodanev@...cle.com>
Date: Tue, 19 Dec 2017 16:59:21 +0300

> LTP/udp6_ipsec_vti tests fail when sending large UDP datagrams over
> ip6_vti that require fragmentation and the underlying device has an
> MTU smaller than 1500 plus some extra space for headers. This happens
> because ip6_vti, by default, sets MTU to ETH_DATA_LEN and not updating
> it depending on a destination address or link parameter. Further
> attempts to send UDP packets may succeed because pmtu gets updated on
> ICMPV6_PKT_TOOBIG in vti6_err().
> 
> In case the lower device has larger MTU size, e.g. 9000, ip6_vti works
> but not using the possible maximum size, output packets have 1500 limit.
> 
> The above cases require manual MTU setup after ip6_vti creation. However
> ip_vti already updates MTU based on lower device with ip_tunnel_bind_dev().
> 
> Here is the example when the lower device MTU is set to 9000:
 ...
> Reported-by: Petr Vorel <pvorel@...e.cz>
> Signed-off-by: Alexey Kodanev <alexey.kodanev@...cle.com>

Applied, thanks Alexey.