VMs Lose Network Connection on WS2012 or WS2012 R2 Hyper-V When Using Broadcom 1GbE NICs

If you’re affected by this issue then you should have read this post. Microsoft posted a KB article for when virtual machines lose network connectivity when you use Broadcom NetXtreme 1-gigabit network adapters on Windows Server 2012 Hyper-V or Windows Server 2012 R2 Hyper-V.

Symptoms

When you have Hyper-V running on Microsoft Windows Server 2012 or Windows Server 2012 R2 together with Broadcom NetXtreme 1-gigabit network adapters (but not NetXtreme II network adapters), you may notice one or more of the following symptoms:

• Virtual machines may randomly lose network connectivity. The network adapter seems to be working in the virtual machine. However, you cannot ping or access network resources from the virtual machine. Restarting the virtual machine does not resolve the issue.
• You cannot ping or connect to a virtual machine from a remote computer.

These symptoms may occur on some or all virtual machines on the server that is running Hyper-V. Restarting the server immediately resolves network connectivity to all the virtual machines.

Cause

This is a known issue with Broadcom NetXtreme 1-gigabit network adapters that use the b57nd60a.sys driver when VMQ is enabled on the network adapter. (By default, VMQ is enabled.)

The latest versions of the driver are 16.2 and 16.4, depending on which OEM version that you are using or whether you are using the Broadcom driver version. Broadcom designates these driver versions as 57xx-based chipsets. They include 5714, 5715, 5717, 5718, 5719, 5720, 5721, 5722, 5723, and 5780.

These drivers are also sold under different model numbers by some server OEMs. HP sells these drivers under model numbers NC1xx, NC3xx, and NC7xx.

Workaround

Broadcom is aware of this issue and will release a driver update to resolve the issue. In the meantime, you can work around the issue by disabling VMQ on each affected Broadcom network adapter by using the Set-NetAdapterVmq Windows PowerShell command. For example, if you have a dual-port network adapter, and if the ports are named NIC 1 and NIC 2 in Windows, you would disable VMQ on each adapter by using the following commands:

Set-NetAdapterVmq -Name “NIC 1″ -Enabled $False
Set-NetAdapterVmq -Name “NIC 2″ -Enabled $False

You can confirm that VMQ is disabled on the correct network adapters by using the Get-NetAdapterVmq Windows PowerShell command.

Note By default, VMQ is disabled on the Hyper-V virtual switch for virtual machines that are using 1-gigabit network adapters. VMQ is enabled on a Hyper-V virtual switch only when the system is using 10-gigabit or faster network adapters. This means that by disabling VMQ on the Broadcom network adapter, you are not losing network performance or any other benefits because this is the default. However, you have to work around the driver issue.

Get-NetAdapterVmqQueue shows the virtual machine queues (VMQs) that are allocated on network adapters. You will not see any virtual machine queues that are allocated to 1-gigabit network adapters by default.