[openstack-dev] [nova][neutron][upgrade] Grenade multinode partial upgrade

Sean M. Collins sean at coreitpro.com
Wed Feb 10 17:52:42 UTC 2016

Ihar Hrachyshka wrote:
> Actually, we already have 1450 for network_device_mtu for the job since:
> https://review.openstack.org/#/c/267847/4/devstack-vm-gate.sh

Ah! Forgot about that one. Cool.

> Also, I added some interface state dump for worlddump, and here is how the
> main node networking setup looks like:
> http://logs.openstack.org/59/265759/20/experimental/gate-grenade-dsvm-neutron-multinode/d64a6e6/logs/worlddump-2016-01-30-164508.txt.gz
> br-ex: mtu = 1450
> inside router: qg mtu = 1450, qr = 1450
> So should be fine in this regard. I also set devstack locally enforcing
> network_device_mtu, and it seems to pass packets of 1450 size through. So
> it’s probably something tunneling packets to the subnode that fails for us,
> not local router-to-tap bits.

Yeah! That's right. So is it the case that we need to do 1500 less the
GRE overhead less the VXLAN overhead? So 1446? Since the traffic gets
enacpsulated in VXLAN then encapsulated in GRE (yo dawg, I heard u like


> I also see br-tun having 1500. Is it a problem? Probably not, but I admit I
> miss a lot in this topic so far.

Dunno. Maybe?

> Also I see some qg-2c68fb65-21 device in the worlddump output from above in
> global namespace. The device has mtu = 1500. Which router does the device
> belong to?..

Good question.

Sean M. Collins

More information about the OpenStack-dev mailing list