/ From:jesse at nicira.com <http://openvswitch.org/mailman/listinfo/discuss>
/>/ 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:pavera at live.com <http://openvswitch.org/mailman/listinfo/discuss>
/>/ CC:discuss at openvswitch.org
<http://openvswitch.org/mailman/listinfo/discuss>
/>/
/>/ On Wed, May 14, 2014 at 8:18 PM, Tom Christensen <pavera at live.com <http://openvswitch.org/mailman/listinfo/discuss>> 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.
/
This can be a pretty common problem when some sort of tunnel (vxlan or gre or
whatever)
is being used to connect physical-to-cloud or production-to-dr or similar
setups - often
you can't control the MTU of the various intervening networks between the two
sides. Is
there a recommended way to encapsulate openvswitch tunnel packets in "something
else" that
will handle the fragmentation/reassembly? Or are there any plans to add
support for
fragmentation/reassembly into openvswitch in the future? Currently I do this
with vyos
openvpn-bridge setups, which fragments/reassembles traffic right up to 9000MTU
inside
tunnels of whatever size. (Yes, it slows the traffic down, but that's life.
There's no
choice in this setup) Wondering if there's a way to do this with openvswitch.
Dave
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