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What is Accelerated Networking?

Article
02/10/2023
4 minutes to read

Accelerated networking enables single root I/O virtualization (SR-IOV) to a VM, greatly improving its networking performance. This high-performance path bypasses the host from the data path, which reduces latency, jitter, and CPU utilization for the most demanding network workloads on supported VM types. The following diagram illustrates how two VMs communicate with and without accelerated networking:

Communication between Azure virtual machines with and without accelerated networking

Without accelerated networking, all networking traffic in and out of the VM must traverse the host and the virtual switch. The virtual switch provides all policy enforcement, such as network security groups, access control lists, isolation, and other network virtualized services to network traffic.

Note

To learn more about virtual switches, see Hyper-V Virtual Switch.

With accelerated networking, network traffic arrives at the VM’s network interface (NIC) and is then forwarded to the VM. All network policies that the virtual switch applies are now offloaded and applied in hardware. Because policy is applied in hardware, the NIC can forward network traffic directly to the VM. The NIC bypasses the host and the virtual switch, while it maintains all the policy it applied in the host.

The benefits of accelerated networking only apply to the VM that it’s enabled on. For the best results, enable this feature on at least two VMs connected to the same Azure virtual network. When communicating across virtual networks or connecting on-premises, this feature has minimal impact to overall latency.

Benefits

Lower Latency / Higher packets per second (pps): Eliminating the virtual switch from the data path removes the time packets spend in the host for policy processing. It also increases the number of packets that can be processed inside the VM.
Reduced jitter: Virtual switch processing depends on the amount of policy that needs to be applied. It also depends on the workload of the CPU that’s doing the processing. Offloading the policy enforcement to the hardware removes that variability by delivering packets directly to the VM. Offloading also removes the host-to-VM communication, all software interrupts, and all context switches.
Decreased CPU utilization: Bypassing the virtual switch in the host leads to less CPU utilization for processing network traffic.

Supported operating systems

The following versions of Windows are supported:

Windows Server 2022
Windows Server 2019 Standard/Datacenter
Windows Server 2016 Standard/Datacenter
Windows Server 2012 R2 Standard/Datacenter
Windows 10, version 21H2 or later (includes Windows 10 Enterprise multi-session)
Windows 11 (includes Windows 11 Enterprise multi-session)

The following distributions are supported out of the box from the Azure Gallery:

Ubuntu 14.04 with the linux-azure kernel
Ubuntu 16.04 or later
SLES12 SP3 or later
RHEL 7.4 or later
CentOS 7.4 or later
CoreOS Linux
Debian “Stretch” with backports kernel, Debian “Buster” or later
Oracle Linux 7.4 and later with Red Hat Compatible Kernel (RHCK)
Oracle Linux 7.5 and later with UEK version 5
FreeBSD 10.4, 11.1 & 12.0 or later

Limitations and constraints

Supported VM instances

Accelerated Networking is supported on most general purpose and compute-optimized instance sizes with 2 or more vCPUs. On instances that support hyperthreading, Accelerated Networking is supported on VM instances with 4 or more vCPUs.

Support for Accelerated Networking can be found in the individual virtual machine sizes documentation.

The list of Virtual Machine SKUs that support Accelerated Networking can be queried directly via the following Azure CLI az vm list-skus command.

Note

Although NC and NV sizes will show in the command below, they do not support Accelerated Networking. Enabling Accelerated Networking on NC or NV VMs will have no effect.

az vm list-skus \
  --location westus \
  --all true \
  --resource-type virtualMachines \
  --query '[].{size:size, name:name, acceleratedNetworkingEnabled: capabilities[?name==`AcceleratedNetworkingEnabled`].value | [0]}' \
  --output table

Custom images (or) Azure compute gallery images

If you’re using a custom image and your image supports Accelerated Networking, make sure that you have the required drivers to work with Mellanox ConnectX-3, ConnectX-4 Lx, and ConnectX-5 NICs on Azure. Also, Accelerated Networking requires network configurations that exempt the configuration of the virtual functions (mlx4_en and mlx5_core drivers). In images that have cloud-init >=19.4, networking is correctly configured to support Accelerated Networking during provisioning.

Sample configuration drop-in for NetworkManager (RHEL, CentOS):

sudo mkdir -p /etc/NetworkManager/conf.d 
sudo cat /etc/NetworkManager/conf.d/99-azure-unmanaged-devices.conf <<EOF 
# Ignore SR-IOV interface on Azure, since it'll be transparently bonded 
# to the synthetic interface 
[keyfile] 
unmanaged-devices=driver:mlx4_core;driver:mlx5_core 
EOF

Sample configuration drop-in for networkd (Ubuntu, Debian, Flatcar):

sudo mkdir -p /etc/systemd/network 
sudo cat /etc/systemd/network/99-azure-unmanaged-devices.network <<EOF 
# Ignore SR-IOV interface on Azure, since it'll be transparently bonded 
# to the synthetic interface 
[Match] 
Driver=mlx4_en mlx5_en mlx4_core mlx5_core 
[Link] 
Unmanaged=yes 
EOF