Port binding records, capabilities and events


There are several cases in the Nova/Neutron/os-vif interaction where the knowledge of the neutron core plugin or ML2 driver would be useful to facilitate a more robust handling of guest networking. For example, 3.

This spec aims to enhance the port binding API via the introduction of a new extension to provide the additional information required to enable Nova and os-vif to make more intelligent use of port binding info.

Please remember os-vif was only intended to remove the VIF plugging process from Nova. The hypervisor configuration (e.g.: libvirt XML generation) is still Nova’s responsibility. Although os-vif removes the networking back-end logic related to the plug and unplug process, Nova still needs to handle the information proposed in this spec.

Problem Description

This spec aims to resolve 3 related problems.

Network connectivity

3 blueprint seeks to enable the use of instances with ip_allocation=none. The port parameter “ip_allocation” was introduced in the 1, to “distinguish the unaddressed port case from the deferred IP allocation case where routed networks is involved” (extracted from 2).

To do this safely and guarantee the guest will have network connectivity, Nova must ensure that the network backend that bound the port provides L2 connectivity.

For example, in a mixed Calico/SR-IOV deployment, it is valid to use ip_allocation=none for any port that is bound by the SR-IOV ML2 driver, but not for the Calico backend. In this case, the only connectivity Calico provides to a guest is L3, therefore is not possible to spawn a VM without an IP address.

Network isolation

In resolving 4, a new config option was required in os-vif to allow enabling VIF isolation for the ML2/ovs backend. As Nova cannot differentiate between VIF_TYPE=”ovs” that is bound by ML2/odl or ML2/ovs it cannot automatically instruct os-vif to enable or disable VIF isolation for ML2/ovs hosts. If the ML2 driver(s) that bound the port are recorded in the port binding details, Nova and os-vif can use that information to more intelligently enable backend specific code paths without requiring additional network backend specific config options.

Bandwidth scheduling

The network driver information can be used too for the bandwidth scheduling featured implemented in Stein, as pointed out in this 6. Currently Nova cannot handle the case where the PF is used by one ML2 driver while the VF is managed by the SR-IOV ML2 driver.

Proposed Change

To address the 3 problems stated above, the following additions to the binding:vif_details dictionary in the port object are proposed:

  • A new connectivity field will be introduced with allowed values of “l2”, “l3” and “legacy”. The “legacy” connectivity value will be the default and is a sentinel to indicate the driver does not support this extension yet and no connectivity info is available. “l2” drivers provide layer 2 connectivity, like for example Linux Bridge, Open vSwitch or SR-IOV. “l3” drivers provide only layer 3 connectivity, like for example Calico 8.

  • A new bound_drivers field will be added that is a dictionary mapping binding_level to driver name. The driver name will be the stevedore entry point name for the driver which is already used in config files and intended to be stable. A POC is available in 7.

To enable declaration of the connectivity, a new property will be added to the ML2 driver base class which will default to “legacy”. ML2 drivers that inherit from this will override the property.

The bound_drivers field will be used by the OVS os-vif plugin to remove the need for 5. We can enable this option only when needed.



binding_details: {
    "connectivity": "l2",
    "bound_drivers": {"0": "openvswtich"}

ML2/odl v1:

binding_details: {
    "connectivity": "legacy",
    "bound_drivers": {"0": "opendaylight"}

ML2/odl v2:

binding_details: {
    "connectivity": "l2",
    "bound_drivers": {"0": "opendaylight_v2"}


binding_details: {
    "connectivity": "l3",
    "bound_drivers": {"0": "calico"}



BP Allow vm to boot without l3 address: https://blueprints.launchpad.net/neutron/+spec/vm-without-l3-address


commit 361455: https://review.openstack.org/#/c/361455/


Boot a VM with an unaddressed port: https://blueprints.launchpad.net/nova/+spec/boot-vm-with-unaddressed-port


bug 1734320: https://bugs.launchpad.net/neutron/+bug/1734320


isolate_vif config option: https://github.com/openstack/os-vif/blob/stable/stein/vif_plug_ovs/ovs.py#L146-L159


review 1: https://review.opendev.org/#/c/623543/40/nova/compute/manager.py@2161


review 2: https://review.openstack.org/#/c/635083


Calico project: https://docs.openstack.org/networking-calico/latest/