1---
2fixes:
3  - |
4    The os-vif OVS plugin now supports using per-port OVS bridges when hybrid plug
5    is not used. This is disabled by default and can be enabled by defining
6    ``[os_vif_ovs]/per_port_bridge=True`` in the compute service nova.conf.
7    This capability should only be enabled if you are deploying with ml2/ovn
8    and experience packet loss during live migrations. This is not supported
9    on windows or when using ironic smartnic ports. This option was introduced
10    to address bug: #1933517. When using OVN as a network backend OVN
11    requires the OVS interface to both have an ofport-id and the neutron port
12    uuid defined in the external_ids field. When the port is plugged if
13    ``[os_vif_ovs]/per_port_bridge`` is not enabled then the OVS port will not
14    be assigned an openflow port id until the tap device is created on the host.
15    On loaded system with many flows and ports it can take a few second for OVN
16    to detect the creation of the tap device and install the correct flows.
17    During that interval packets can be dropped.
18    When ``[os_vif_ovs]/per_port_bridge`` is enabled, os-vif will add the VM tap
19    device to a new bridge that is connected to the integration bridge via a
20    patch port. This enables OVN to install the openflow rules on the
21    integration bridge before the tap is created reducing the possibility for
22    packet loss during a live migration. By default per port bridges are disabled
23    and this feature is considered experimental, however it will likely be enabled
24    by default in the future after we gain experience with how this bridge topology
25    scales in larger deployments.
26