Hardware offloading


As of the 20.05 release, the OpenStack charms support configuration of Open vSwitch hardware offloading with Mellanox ConnectX-5 NICs. Hardware offloading can be used to accelerate VLAN and VXLAN networking using the capabilities of the underlying network card to achieve much higher performance than with virtio based VM ports.

See the Neutron documentation on OVS hardware offload for background information.

For OVN-specific information on hardware offloading see the OVN page.


Hardware offloading cannot be used with either SR-IOV or DPDK networking support as provided by the OpenStack charms.


  • Ubuntu 18.04 LTS or later

  • Linux kernel >= 5.3

  • Open vSwitch >= 2.11

  • OpenStack Stein or later

  • Mellanox ConnectX-5 NICs using recent firmware (>= 16.26.4012)


Hardware offload does not currently support offloading of Neutron Security Group rules - experimental support is expected in Open vSwitch 2.13 when used with Linux >= 5.4 and as yet unreleased NIC firmware. It is recommended that port security is disabled on Neutron networks being used for hardware offloading use cases due to the performance overhead of enforcing security group rules in userspace.


MAAS - Hardware Enablement Kernel

As a more recent Linux kernel than that provided as part of Ubuntu 18.04 LTS is required to support this feature, machines with compatible network cards must be commissioned and configured in MAAS to use the Ubuntu 18.04 LTS Hardware Enablement (HWE) kernel rather than the standard release kernel.


Mellanox SR-IOV VF-LAG provides hardware link-aggregation (LAG) for hardware offloaded ports and is recommended for deployment as it avoids the need to pass two hardware offloaded ports to each VM for resilience. This feature is configured in the underlying NIC using standard Linux bonding as configured through MAAS.


VF-LAG can only be used with NIC ports that reside on the same underlying NIC.


Use of VF-LAG reduces the offloaded port capacity of the card by 50%.

Charm configuration

Hardware offload support is enabled using the enable-hardware-offload option provided by the neutron-api and neutron-openvswitch charms.

Enabling hardware offloading requires configuration of VF representator ports on the NICs supporting the hardware offload - these are used to route network packets without flow rules to the OVS userspace daemon for handling and subsequent programming into the hardware offloaded flows. This is supported via use of the sriov-numvfs option provided by the neutron-openvswitch charm.

Finally the openvswitch firewall driver must be used with hardware offloading. Eventually it will be possible to offload security group rules using this driver (see note above).

The following overlay may be used with the OpenStack base deployment bundle:

series: bionic
    charm: cs:neutron-openvswitch
      enable-hardware-offload: true
      sriov-numvfs: "enp3s0f0:32 enp3s0f1:32"
      firewall-driver: openvswitch
    charm: cs:neutron-api
      enable-hardware-offload: true
      pci-passthrough-whitelist: '{"address": "*:03:*", "physical_network": null}'

In this overlay enp3s0f0 and enp3s0f1 are two ports on the same Mellanox ConnectX-5 card and are configured as a Linux bond bond1 to enable VF-LAG for resilience and performance. bond1 is also configured with the network interface used for VXLAN overlay traffic to allow full offloading of networks of this type.

The nova-compute charm is configured to use the VF functions provided by the network cards using the pci-passthrough-whitelist option. The above example demonstrates configuration for VXLAN overlay networking.


After deploying the above example the machines hosting neutron-openvswitch units must be rebooted for the changes to take effect.

Creating hardware offloaded ports

Hardware offloaded ports must be created via Neutron and then passed to Nova for use by VMs:

openstack port create --network private --vnic-type=direct \
     --binding-profile '{"capabilities": ["switchdev"]}' direct_port1
openstack server create --flavor m1.small --image bionic \
     --nic port-id=direct_port1 vm1

The image used for the VM must include the Mellanox kernel driver. Ubuntu 18.04 LTS (or later) cloud images include this driver by default.