Comment 4 for bug 1402046

Usually, GRE tunnel MTU should be (Host MTU - 24 - 20) to allow clients to
use Jumbo frames. If HOST MTU=9000, then guest MTU should be = 8956

--
Best regards,
Sergii Golovatiuk,
Skype #golserge
IRC #holser

On Sun, Dec 14, 2014 at 7:36 PM, Alexei Sheplyakov <<email address hidden>
> wrote:
>
> > Currently, we are facing issues with neutron ovs agent and GRE tunnels.
> At least for our Ubuntu version which has
> > 2.0.2 version of kernel module and userspace we can see that packets
> more than 1458 bytes cannot get through.
>
> I think this behavior is correct: ovs tries to avoid fragmentation of the
> outer IPv4 packets. The packets larger than
> GRE tunnel MTU (1456 == 1500 - 24 - 20) must be fragmented by the guest OS
> itself. To make this work neutron
> should pass the correct MTU value (<= 1456) to instances attached to GRE
> tunnels.
>
> --
> You received this bug notification because you are a member of Fuel
> Library Team, which is a bug assignee.
> https://bugs.launchpad.net/bugs/1402046
>
> Title:
> OpenvSwitch agent sets DF flag for GRE tunnels breaking instances
> connectivity
>
> Status in Fuel: OpenStack installer that works:
> In Progress
> Status in Fuel for OpenStack 6.0.x series:
> In Progress
> Status in Fuel for OpenStack 6.1.x series:
> Triaged
>
> Bug description:
> Currently, we are facing issues with neutron ovs agent and GRE
> tunnels. At least for our Ubuntu version which has 2.0.2 version of
> kernel module and userspace we can see that packets more than 1458
> bytes cannot get through. This happens because for some reason gre
> tunnels are created with df_inherit and df_default flags set to true.
>
> Disabling them fixes the issue completely.
>
> It seems we need to apply the patch that sets dont_fragment option to
> false into agent section of neutron plugins config along with setting
> df_inherit to false in neutron code.
>
> I am not sure if we need to set Centos df_inherit flag to false (as
> long as I am not sure it exists for OVS 1.10), but it seems we also
> need to set df_default to false for centos installation.
>
> For ubuntu we need to add the same string in
>
> /usr/lib/python2.7/dist-packages/neutron/agent/linux/ovs_lib.py
>
> 232: vsctl_command.append(("options:df_inherit=%s" %
> bool(dont_fragment)).lower())
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/fuel/+bug/1402046/+subscriptions
>