[ovs-dev] [PATCH] dpif-netlink-rtnl: Retry a smaller MTU for netdev when MAX_MTU is too large.

Yifeng Sun pkusunyifeng at gmail.com
Fri Jul 6 18:24:22 UTC 2018

Hi Ben,

Yes, this is GRE-specific, somehow gre_sys doesn't support current MTU which
is 65000.

`make check-kmod` no. 11 and 21 fail due to this issue.

On the kernel side, the error shows up as:
[ 6135.119999] gre_sys: Invalid MTU 65000 requested, hw max 1500

It reflects to userspace as error below:
dpif_netlink_rtnl|WARN|setting MTU of tunnel gre_sys failed (Invalid


On Fri, Jul 6, 2018 at 10:58 AM, Ben Pfaff <blp at ovn.org> wrote:

> On Thu, Jul 05, 2018 at 11:55:46AM -0700, Yifeng Sun wrote:
> > When MAX_MTU is larger than hw supported max MTU,
> > dpif_netlink_rtnl_create will fail. This leads to
> > testing failure '11: datapath - ping over gre tunnel'
> > in 'make check-kmod'.
> >
> > This patch fixes this issue by retrying a smaller MTU
> > when MAX_MTU is too large.
> >
> > Signed-off-by: Yifeng Sun <pkusunyifeng at gmail.com>
> Is this GRE-specific?  (Why would only GRE care about large MTUs?)

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