MTU has been changed in neutron to 1450 by default by [0] As result ISCSI job on xenial become broken. With this patch PUBLIC_BRIDGE_MTU is set to smallest mtu of existed interfaces decreased by 50. MTU on IRONIC_VM_NETWORK_BRIDGE is set to PUBLIC_BRIDGE_MTU. [0] https://github.com/openstack/neutron/commit/51a697817da849c8f9dae9651f17cd863e170fdc Closes-Bug: #1631875 Related-Bug: #1603268 Change-Id: I044d415410a714591e9770a57cfb8509a103cf00