IPv6 problem on VM Windows with VirtIO (paravirtualized) network adapter

[fabienfs]

Hello,

I have a problem on several VMs running with Windows (Windows Server 2022 or Windows 10) regarding IPv6 connectivity in my Proxmox VE 7.3.4.
Indeed, on each VM I have a network device in model VirtIO (paravirtualized).

The guest agent (virtio-win-0.1.173-2) is installed on Windows.

When I define in Windows an IPv4 and IPv6 address, no problem with the IPv4 connectivity, but with IPv6 I have strange phenomena : I can't ping the gateway. I have to shut down the VM, change the network card model from VirtIO to Intel E1000, restart the VM, reconfigure the IPv6 address, then I ping successful the gateway (and internet), then I have to stop the VM, change the model of the network card again from Intel E1000 to VirtIO, and then no more problem: IPv6 works.

I had this same problem on several Windows VMs and therefore both Windows Server 2022 and Windows 10.

However, it happens after a few days that I sometimes have IPv6 disconnections with VirtIO and then it works again afterwards.

It therefore seems that there are stability issues with VirtIO, IPv6 and Windows VMs.

Has anyone seen this problem before?

Also: I'm surprised (but maybe it's normal), that my VirtIO network card shows 10Gbps connectivity while I'm on 1Gbps (please see the screenshot in attach) ?

thanks
Fabien

 

[bedjer]

Same here.
For some VM, I can use the VirtIO network card and all works fine at 10gbps with both IPV4 and IPV6
For some other VMs, IPV6 does not communicate at all, and I must revert to either the E1000 or VMXNet3 to get IPV6 to communicate properly. But limited to 1gbps.

Migrations from VMWare or clean Windows installs ; it does not seem to care.
Issue is totally hit or miss. Once a VM decides not to allow IPV6 using VirtIO, there appears to be no way to make it work other than rollbacking to e1000.

I tried with the stable release - virtio-win-0.1.240.iso
Also with the early release - virtio-win-0.1.248.iso

Tried with Win10, Win11 ==> 7 VMs with failures out of 11 total.
Windows servers 2016,2019,2022 ==> 1 failures so far out of 13 vms

Same issue exists on multiple hosts. Using Dell R730 over here.

No issues on my Linux VMs.

As writing these lines I realize all machines with the issue are not using any VLAN TAGS
As soon as I assign a VLAN tag, IPV6 starts to work ; but on the wrong network obviously.