[Bug 1674307] Re: Neutron v9 jumbo frames support

[James Page]

I've just redeployed a cloud onto Xenial/Ocata in a similar
configuration; the instances running on the cloud all get the higher MTU
as configured by neutron, irrespective of the MTU on the tunnel bridge.

I've confirmed this using iperf to assess performance between units
including mismatched MTU configurations/reality.

In terms of charm configuration using:

juju config neutron-api network-device-mtu=9000
juju config neutron-gateway instance-mtu=8500

should not be required any longer; if you just set global-physnet-
mtu=9000 neutron will do the maths to figure out overlay overheads and
drop MTU's for network segments as appropriate.

Just as a side note; the versions referenced in the original bug report
are Newton versions, not Ocata versions - maybe there is a different in
function between the two releases.

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https://bugs.launchpad.net/bugs/1674307

Title:
  Neutron v9 jumbo frames support

Status in neutron package in Ubuntu:
  Incomplete

Bug description:
  Hi Guys

  I just recant deployed openstack ocata using ubuntu-16.04, MAAS 2.1.3
  and JUJU charm,

  All my servers are set to use MTU=9000 on all connected
  interfaces(setting propagated via MAAS/DHCP)

  I have set configuration flags in neutron-api charm to reflect MTU
  size, yet when i create networks its always uses MTU=1500

  juju config neutron-api path-mtu=8600
  juju config neutron-api global-physnet-mtu=9000
  juju config neutron-api network-device-mtu=9000
  juju config neutron-gateway instance-mtu=8500

  When check interface MTU (phisical interface) all systems are
  reporting jumbo size (9000).

  One thing i have spotted when checked OVS bridges the br-tun bridge
  MTU is only 1500

  The behaviour is exactly same in both overlay setups vxlan/gre.

  
  2: eno1: mtu 9000
  3: eno2: mtu 9000
  4: eno3: mtu 9000
  5: eno4: mtu 9000
  6: enp4s0: mtu 9000
  7: enp5s0: mtu 9000
  8: bond0: mtu 9000
  9: bond1: mtu 9000
  10: br-bond0: mtu 9000
  11: ovs-system: mtu 1500
  12: br-int: mtu 1450
  13: br-ex: mtu 9000
  14: br-tun: mtu 1500
  15: lxdbr0: mtu 1500

  
  JUJU app versions

  neutron-api 9.0.0
  neutron-gateway 9.0.0
  neutron-openvswitch 9.0.0
  nova-cloud-controller 14.0.2
  nova-compute 14.0.2

  Any assistance in fixing this will be greatly appreciated.

  Thanks 
  Piotr

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