I have a Windows 11 Enterprise LTSC host running Hyper-V with an external virtual switch. The VM provides DHCP, DNS, and WDS services. Other VMs connected to the external switch, as well as the host adapter used by the switch, receive DHCP addresses normally. However, physical devices connected through a basic unmanaged Netgear switch do not receive an address. They can communicate with the VM when assigned a static IP, but DHCP renewal times out.
I have tried disabling the firewalls, setting the networks to Private, changing the host's physical adapter, enabling MAC spoofing, confirming that DHCP Guard and Router Guard are disabled, and disabling NIC sharing. There are no VLANs involved; the laptop and host are connected through the unmanaged switch.
A packet capture on the VM shows the DHCP requests arriving and the offers being sent. A capture on the Hyper-V host also shows the offers on both the physical adapter and the virtual bridge, but the physical client never receives them. What should I check next?
2 Answers
Run Wireshark on the physical laptop while renewing its lease. If it sees the DHCPDISCOVER but not the DHCPOFFER, the capture confirms the problem is on the Layer 2 path after the VM responds. Testing with a different physical switch, a direct cable, or another host NIC can quickly isolate whether the unmanaged switch or the host adapter is discarding the return broadcast.
Double-check the external switch binding rather than only checking that it says External. Make sure it is attached to the physical Ethernet adapter actually connected to the switch, and inspect that adapter's Hyper-V extensions, VLAN configuration, filtering settings, and vendor driver. Updating or replacing the physical NIC driver is also worth trying, since some adapters or drivers mishandle bridged broadcast traffic.
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