> From: [email protected]
> Date: Thu, 15 May 2014 14:43:12 -0700
> Subject: Re: [ovs-discuss] MTU/fragmentation issue in 2.0.1/openstack
> icehouse using GRE
> To: [email protected]
> CC: [email protected]
>
> On Wed, May 14, 2014 at 8:18 PM, Tom Christensen <[email protected]> wrote:
> > I'm seeing an issue in openstack icehouse running on ubuntu 14.04, ovs
> > version 2.0.1, package version 2.0.1+git20140120-0ubuntu2 where gre packets
> > cannot pass between 2 ovs bridges (br-int and br-tun) when the original
> > source packet is larger than 1438 bytes (mtu set to 1500 everywhere). I've
> > confirmed that openstack havana running on ubuntu 12.04 (ovs 1.10.2) does
> > not have this same issue, so it feels like a regression. I don't know where
> > this should be reported, or if its been fixed in subsequent versions of
> > openvswitch.
> >
> > I also am pretty new to openvswitch so, any help in really nailing down
> > exactly what is going on inside these bridges would be appreciated greatly.
>
> Tunnel fragmentation isn't really supported well in OVS and even in
> cases where it does work it performs poorly. It is best if you either
> increase the MTU on the physical network or decrease it in the sending
> VMs.
I have attempted decreasing the mtu in the VMs, this does not work in 2.0.1. I
can see that the packet is fragmented on the tap interface, and there aren't
any packets leaving the VM larger than 1438 bytes (I set the MTU to 1400), but
they still don't get out of the br-int bridge.
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