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