On Tuesday, December 20, Microsoft released an emergency patch to fix problems caused by updates released the previous week in December’s Patch Tuesday. Some users reported being unable to create virtual machines on Hyper-V hosts.
Resolution: This issue was resolved in out-of-band (OOB) updates released December 20, 2022 for installation on all Hyper-V hosts in your environment which are using Software Defined Networking (SDN) and managed by System Center Virtual Machine Manager (SCVMM). You do not need to install any update or make any changes to other servers or client devices in your environment to resolve this issue. – Microsoft Windows Health Dashboard
Only Windows Server 2019 and Windows Server 2022 should be impacted after installing December 2022 Patch Tuesday updates (KB5021237 and KB5021249).
The updates were released December 13th, you don’t need to roll these back to get the fix, simply install KB5022553 / KB5022554 on top of that update. Prioritize systems using SDN managed by SCVMM, then schedule updating your other Hyper-V installations for consistency.
For the scripts for large-scale deployments on the SCVMM Management Server and further details on applying the workaround, refer to this support article: Win12B issue in System Center Virtual Machine Manager
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Software Defined Networking (SDN) managed by SCVMM might have issues with new VMs