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

[David Miller <davem@davemloft.net>]

From: Alexey Kodanev <alexey.kodanev@oracle.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@suse.cz>
> Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>

Applied, thanks Alexey.