2026.1 Series Release Notes

4.3.0-3

Bug Fixes

• Tap devices created by the Open vSwitch plugin (when Neutron requests ovs_create_tap) now have IPv6 disabled before they are brought up. The tap is given the instance’s MAC address, so with IPv6 enabled the host derived the instance’s own link-local address for it and ran duplicate address detection for that address; the resulting neighbour solicitation was queued towards the guest, whose own duplicate address detection could then mark its link-local address dadfailed and leave IPv6 on that interface unusable.

  This disables only the host’s IPv6 stack on the tap, not IPv6 traffic forwarded to or from the instance. Guest IPv6 remains enabled. The fix applies to newly created tap devices; existing devices are not reconfigured until recreated through the normal instance lifecycle.

4.3.0

New Features

• Added support for os-vif to pre-create TAP devices when using OVS/OVN. The VIFPortProfileOpenVSwitch object now supports two new fields:

  • create_tap: When set to True, os-vif will create the TAP device with the correct MAC address and MTU before adding it to OVS.

  • multiqueue: When set to True along with create_tap, the TAP device will be created with multiqueue support enabled for improved performance with multiple vCPUs. The multiqueue setting is determined by Nova from the hw:vif_multiqueue_enabled flavor extra spec or image property.

  When the [ovn]/ovs_create_tap config option is enabled in Neutron’s ML2/OVN mechanism driver, Neutron sets the ovs_create_tap flag in the vif_details during port binding. Nova then reads this value and propagates it to os-vif via the create_tap field, and configures libvirt with managed="no" so it uses the pre-created TAP device. This reduces live migration downtime by ensuring the network is fully wired before the VM starts.

  See bug 2069718.