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?
4 Answers
A different VLAN would require DHCP relay, but you said this is a flat network with no VLANs. An ordinary unmanaged switch does not need to know where the DHCP server is; it simply forwards the broadcast. If static clients work but DHCP offers do not, focus on broadcast handling or filtering rather than DNS, routing, or the default gateway.
Since the VM is receiving the DHCPDISCOVER and generating a DHCPOFFER, the DHCP service itself is probably fine. The failure is somewhere between the Hyper-V virtual switch, the host's physical NIC, and the unmanaged switch. Capture traffic on the physical client as well as the VM and host, then compare the transaction ID and destination MAC address. That will show whether the offer is leaving the host but being filtered or dropped before reaching the client.
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.
Related Questions
Can't Load PhpMyadmin On After Server Update
Redirect www to non-www in Apache Conf
How To Check If Your SSL Cert Is SHA 1
Windows TrackPad Gestures