I'm running Windows 11 Enterprise LTSC with Hyper-V. The host has an External virtual switch connected to the physical network adapter, and the VM provides DHCP, DNS, and WDS services. Other VMs using that switch can obtain addresses, and the host's adapter can also receive a lease from the VM. However, physical devices connected through a basic unmanaged switch never receive an address. If I assign them static IPs, they can ping the VM, but DHCP renewal times out.
I've tried disabling the firewalls, setting the networks to Private, using another physical adapter, enabling MAC spoofing, confirming DHCP Guard and Router Guard are disabled, and disabling NIC sharing. There are no VLANs involved; the test setup is simply a laptop connected to the host through an unmanaged Netgear switch.
A packet capture on the VM shows the client's DHCP request arriving and the server's offer being sent. A capture on the Hyper-V host also shows the offer on both the physical adapter and the virtual bridge adapter, but the physical client never receives it. What could be blocking the DHCP response between the host and the physical device?
3 Answers
This doesn’t sound like a VLAN or DHCP relay issue in the setup you described. An unmanaged switch should simply forward the DHCP broadcasts. Since the VM sees the request and generates a reply, recheck the external switch configuration and NIC properties, then test with the host connected directly to one client to eliminate the physical switch and cabling from the path.
Confirm the packet path with captures on both ends: the VM, the host’s physical adapter, and the client. DHCP uses broadcast traffic, so a normal ping working with static addresses doesn’t prove that DHCP broadcasts are being forwarded correctly. If the offer is visible on the host adapter but not on the client, focus on the physical NIC, its driver, and the Hyper-V switch binding.
The key clue is that the request reaches the VM and the offer leaves it, but the client never sees the response. That points away from the DHCP service itself and toward the Hyper-V external-switch bridge or the host’s physical NIC path. Verify that the external switch is actually bound to the adapter connected to the unmanaged switch and that no host networking or security software is filtering bridged broadcast traffic.
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