[openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

Fredy Neeser Fredy.Neeser at solnet.ch
Fri Mar 6 17:01:08 UTC 2015

Hello world

I recently created a VXLAN test setup with single-NIC compute nodes 
(using OpenStack Juno on Fedora 20), conciously ignoring the OpenStack 
advice of using nodes with at least 2 NICs ;-) .

The fact that both native and encapsulated traffic needs to pass through 
the same NIC does create some interesting challenges, but finally I got 
it working cleanly, staying clear of MTU pitfalls ...

I documented my findings here:


For those interested in single-NIC setups, I'm curious what you think 
about [1]  (a small patch is needed to add "VLAN awareness" to the 
qg-XXX Neutron gateway ports).

While catching up with Neutron changes for OpenStack Kilo, I came across 
the in-progress work on "MTU selection and advertisement":

   [3]  Spec: 
   [4]  Patch review:  https://review.openstack.org/#/c/153733/
   [5]  Spec update:  https://review.openstack.org/#/c/159146/

Seems like [1] eliminates some additional MTU pitfalls that are not 
addressed by [3-5].

But I think it would be nice if we could achieve [1] while coordinating 
with the "MTU selection and advertisement" work [3-5].


- Fredy

Fredy ("Freddie") Neeser

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