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How to force the Guest VM synthetic NIC not to intercept DHCP Discover packets when SR-IOV is enabled?

PagodaEnterprises 0 Reputation points
2024-08-08T08:05:32.7033333+00:00

Windows Server 2022 with Hyper-V role and SET with SR-IOV enabled and all Switch Extensions disabled on Mellanox NICs.

Guest VM is version 2. IOV pairs requested is set to 4 and the VM receives 4.

Guest OS will not receive DHCP address when NIC is SR-IOV enabled. We tried Windows and Linux based OS and it seems that this issue is agnostic to the Guest OS:

  1. Network capture from the router shows that Guest OS will send IPv6 multicast packets via the SR-IOV adapter. No IPv4 DHCP request packets are observed.
  2. Capture from the synthetic NIC of the Guest OS shows DHCP Discover packets. If the same capture is done on the currently bridged SR-IOV adapter, there are no DHCP Discover packets captured. Only IPv6 multicast.
  3. When SR-IOV is disabled - DHCP address can be obtained and networking works nominally.
  4. When SR-IOV is enabled and when static IPv4 is used - all networking works nominally.

It can be safely assumed that the Guest VM synthetic NIC is set to always capture DHCP Discover packets, even when it is not configured to do so (we checked that the DHCP guard is disabled) and when the Guest VM NIC is in SR-IOV mode, the intercepted DHCP requests seems to be dropped or discarded somewhere else.

How to force the Guest VM synthetic NIC not to intercept and redirect/drop/discard the DHCP packets when SR-IOV is enabled?

Hyper-V
Hyper-V
A Windows technology providing a hypervisor-based virtualization solution enabling customers to consolidate workloads onto a single server.
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  1. Ian Xue 36,751 Reputation points Microsoft Vendor
    2024-08-14T02:13:53.2933333+00:00

    Hi PagodaEnterprises,

    Hope you're doing well.

    Ensure that the relevant network parameters and policies are correctly set in the network configuration of the virtual machine. Check the virtual machine's network adapter settings to confirm that it is compatible with the host's network environment.

    Second, check the network services and firewall settings of the virtual machine's operating system. Ensure that the network service is operating properly and that the firewall is not intercepting DHCP discovery packets by mistake. Firewall rules may need to be adjusted to allow relevant packets to pass through.

    If the problem persists, you can try updating the hypervisor and related drivers.

    Best Regards,

    Ian Xue

    If the Answer is helpful, please click "Accept Answer" and upvote it.

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