Hyper-V UEFI PXE BOOT Response limits

Question

I was working with a customer that was moving from a DHCP network that was on a Layer 3 isolated VLAN with IP Helpers to their PXE environment, over to a Layer 2 environment with all the PXE servers and machines on the same Layer 2 vlan. All the machines were gen2 Hyper-v machines booting with UEFI pxe. Once we cutover we noticed machines would hang during the dhcp pxe process. Doing wireshark traces we saw the requests, and responses, but there were no ACK from the client. As a test we shut down all PXE services except for 1 and the machines immediately were able to boot. They continued to boot up to 3 PXE machines running. As soon as we started the 4th machines would hang booting. It didn't matter which 3 of the total of 6 machines we had running. It would work with up to 3, but after that nothing. It is acting like the hyper-v UEFI boot environment would get flooded with too many pxe responses, and would hard lock. This seems like a bug with the hyper-v UEFI environment. Unfortunately there is no real way to capture logs from the UEFI engine. Has anyone else seen issues with this? It worked previously because we believe the ip-helpers for the Layer 3 network were isolating the broadcasts from the hosts. But now that they have direct broadcast there is just too much information for the hyper-v to handle.

Answer 1

Hi,

What is the version of the Hyper V server? Also, check if the Hyper V host installed the latest Windows Update, if not, please update the Hyper V host.

You may check if the issue occurs on Gen1 VMs.

Actually, there's some discussion about Hyper V Gen2 VM boot issue with PXE boot, for your reference:

https://social.technet.microsoft.com/Forums/en-US/436c67cb-1c7d-4c5f-8f62-3518a0cfaeb4/hyperv-build-1703-generation-2-pxe-has-faulty-arp-implementation?forum=winserverhyperv

Thanks for your time!
Best Regards,
Anne

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