Strict minimum bandwidth support for tunnelled networks

Launchpad bug:

The aim of the RFE is to improve the previous implemented RFE Strict minimum bandwidth support [1].

Problem Description

Since [1], Neutron has the ability to model the available bandwidth of the physical interfaces (ingress and egress) connected to the physical networks (flat and VLAN networks). This information is collected by Placement and used to spawn virtual machines with network ports on compute nodes with enough bandwidth. That guarantees a minimum port throughput.

This feature is currently implemented in three backends: ML2/SR-IOV, ML2/OVS and ML2/OVN. The full list of related patches can be reviewed at [2].

However, most of the current deployments do not use physical backed networks (flat or VLAN) but overlay networs (VXLAN and Geneve). Of course those deployments use ML2/OVS and ML2/OVN; ML2/SR-IOV does not support tunnelled networks. That leads to an existing gap in the currently implemented feature: there is no way to model tunnelled networks.

Proposed Change

This RFE proposes a way to model the available bandwidth for tunnelled networks in compute nodes. This implementation will be limited to ML2/OVS and ML2/OVN backends.

The referred backends handle the overlay traffic sending and receiving this traffic from a host interface, that acts as a VTEP [3]. This host interface is identified by an IP address, known as “local_ip” in the ML2 plugin configuration file [4].

This RFE proposes to use the same configuration options provided in [1], adding a static string constant to define a resource provider in Placement that could be configurable by the administrator. This string will be the suffix of the resource provider name, same as Neutron uses the physical bridge names to build their resource provider names. For example “u20ovn:OVN Controller agent:rp_tunnelled”, being “rp_tunnelled” the provided string. The default value will be “rp_tunnelled”. This configuration variable will be stored in the [ml2] section and will be accesible from the Neutron server and the OVS agent:

tunnelled_network_rp_name = custom_rp_name  # "rp_tunnelled" by default.

Example of ML2/OVS configuration section:

resource_provider_bandwidths = br0:EGRESS:INGRESS,rp_tunnelled:EGRESS:INGRESS

Example of ML2/OVN configuration, stored in the local database of the OVS service:

root@u20ovn:~# ovs-vsctl list open_vswitch .
external_ids : {hostname=u20ovn,

Note that in ML2/OVN, it is mandatory to define the tunnelled resource provider assignation to the host in the “resource_provider_hypervisors” list.

This new string constant cannot be used as a physical bridge name. To avoid any possible clash, there will be a new check when parsing the physical network bridge mappings.

A host with ML2/OVN backend with a physical network (mapped to the physical bridge “br-ex”) and a tunnelled network will report the following resource provider tree:

$ openstack resource provider list
| uuid                                 | name                                     | generation | root_provider_uuid                   | parent_provider_uuid                 |
| 8f0e060d-bf63-42a1-85e6-710c8b2fccc8 | u20ovn                                   |         10 | 8f0e060d-bf63-42a1-85e6-710c8b2fccc8 | None                                 |
| cb101b60-527b-5264-8e7f-213c7b88e9e1 | u20ovn:OVN Controller agent              |          1 | 8f0e060d-bf63-42a1-85e6-710c8b2fccc8 | 8f0e060d-bf63-42a1-85e6-710c8b2fccc8 |
| 521f53a6-c8c0-583c-98da-7a47f39ff887 | u20ovn:OVN Controller agent:br-ex        |         20 | 8f0e060d-bf63-42a1-85e6-710c8b2fccc8 | cb101b60-527b-5264-8e7f-213c7b88e9e1 |
| dfdbf43f-f60b-577c-bae8-3dcea448c735 | u20ovn:OVN Controller agent:rp_tunnelled |          6 | 8f0e060d-bf63-42a1-85e6-710c8b2fccc8 | cb101b60-527b-5264-8e7f-213c7b88e9e1 |

A new static trait will be added to represent this resource provider: “CUSTOM_NETWORK_TUNNEL_PROVIDER”. This is what identify that this resource provider is for tunnelled networks. E.g.:

$ openstack resource provider trait list $rp_tun
| name                             |
| CUSTOM_VNIC_TYPE_VDPA            |

This is an example of a port resource request, sent to Nova when creating a virtual machine. The port has a minimum bandwidth rule of 500 kbps, egress direction:

port['resource_request'] = {
    'request_groups': [
        {'id': 'c51c6f07-8e01-548c-9756-d5e54a780bb6',
         'resources': {'NET_BW_EGR_KILOBIT_PER_SEC': 500}
    'same_subtree': ['c51c6f07-8e01-548c-9756-d5e54a780bb6']


This spec is not considering the case of shared resource providers. For example when the same interface is shared between a VLAN/flat network and and overlay network. What this spec is proposing is to provide the scheduling functionality to ports in overlay networks. In case of having shared resources, the administrator will need to split bandwidth assignation between resource providers. Currently Placement API nor Neutron cannot provide a way to model a shared resource.


This RFE does not introduce any API change.

Data Model Impact

This RFE does not introduce any model change.

Security Impact


Performance Impact


Other Impact

Currently there is no support for minimum bandwidth QoS rules for tunnelled networks, neither in Placement nor in the ML2 backend (OVS, OVN). However, it is possible to have ports with those type of QoS rules (maybe inherited from the network QoS policy). With this feature, the minimum bandwidth QoS rules won’t be discarded, like now, when the port resource request is built (that is the Placement blob to request a specific bandwidth in a specific network).

A new check will be added to inform about those ports located on tunnelled networks with minimum bandwidth QoS rules. The output of this check will be a log with the list of ports, their networks and QoS policies. This spec is considering the current Neutron implementation:

  • ML2/OVS rejects the assignation of a QoS policy with minimum bandwidth rules and prevents from binding a port with them.

  • The ML2/OVN mechanism driver implemented the minimum bandwidth rule support recently and does not prevent this scenario. However this functionality was implemented in Zed release; it is unlikely that many deployments are in this state (with ports located in overlay networks with QoS policies and minimum bandwidth rules).

This spec does not consider the rebuild of the current allocations. Any port already present in a host that creates a new resource provider for tunnelled networks, won’t be allocated. Once there is standard a procedure to perform this action, a new spec/bug will be created to track this improvement, but this is out of scope in this spec.

Part of this RFE will be to document the alternatives the user has to, in case of having a port with minimum bandwidth rules before enabling this feature, create the needed allocations:

  • Live migrate the VM with the port. That will trigger the Placement scheduling and the allocation creation.

  • Detach and attach again the port to the VM. That will have the same effect. This functionality was added to Nova in Wallaby.



Primary assignees:

Rodolfo Alonso Hernandez <> (IRC: ralonsoh)

Work Items

  • ML2 plugin update.

  • Migration script to log those existing ports with minimum bandwidth rules in tunnelled networks.

  • Documentation, including the methods to re-created the allocations for pre- created ports.

  • Tests and CI related changes.


  • Unit/functional tests.

  • Fullstack tests: increase the current fullstack tests coverage to check this new feature.

  • Tempest tests: create a VM with a minimum bandwidth port, update the QoS policy and minimum bandwidth rule limits, unset the QoS policy, migrate the VM.

Documentation Impact

User Documentation

Ammend the “Strict minimum bandwidth support” [1] documentation, adding this new improvement.