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Critical Hyper-V SET Switch Bug: Switch Randomly Changes to Internal After Reboot on Windows Server 2025

Krasimir Rangelov 210 Reputation points
2025-02-15T20:25:53.4533333+00:00

Dear Microsoft Learn community,

I'm facing a critical and highly concerning issue with the Hyper-V Switch Embedded Teaming configuration on my Windows Server 2025 failover cluster. After rebooting the Hyper-V virtualization host, the SET switch unexpectedly changes from External to Internal, leaving all other network adapters in a state where they obtain their own IP addresses via DHCP or APIPA.

What makes this worse is that the SET switch remains Internal, but all VMNetworkAdapters assigned to the Management OS are still present. There is no way to revert the configuration except to delete and completely recreate the SET switch, which is highly disruptive.

This issue has now affected two of my Hyper-V failover cluster nodes running Windows Server 2025. I have tried multiple approaches to resolve or prevent this, but nothing seems to work. Searching online did not return any useful information regarding this behavior.

Right now, I am away from my servers and cannot access them remotely because they have lost all connectivity. My Live Migration traffic, VLAN configurations, and all dependent networking services are broken due to this issue, and I suspect the entire cluster is in a failed state.

This has happened three times already, and I have no clue why. Before moving to SET, I was using LBFO, and I never encountered such problems.

Has anyone else experienced this issue with Hyper-V SET on Windows Server 2025?

  • Are there any known fixes or workarounds?
  • Could this be a bug in Windows Server 2025, anything from 2022 or even 2019?

Any insights or solutions would be greatly appreciated!

Windows Server
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A family of Microsoft server operating systems that support enterprise-level management, data storage, applications, and communications.
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A Windows technology providing a hypervisor-based virtualization solution enabling customers to consolidate workloads onto a single server.
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Windows: A family of Microsoft operating systems that run across personal computers, tablets, laptops, phones, internet of things devices, self-contained mixed reality headsets, large collaboration screens, and other devices.Network: A group of devices that communicate either wirelessly or via a physical connection.
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  1. Ian Xue 39,471 Reputation points Microsoft Vendor
    2025-02-19T03:38:08.23+00:00

    Hi Krasimir Rangelov,

    Thanks for your post. Please understand that there is limited resource for Hyper-V known issue in Windows server 2025. 

    For testing purposes, please add an additional Internal switch via Hyper-V "Virtual Switch Manager" and gave it a name of "Static Switch". Then changed it's settings via Control Panel->Network and Internet->Network and Sharing Center->Change adapter settings. Right click on the new adapter and select Properties->Internet Protocol Version 4 (TCP/IPv4) and set a static IP that is not currently used on your network, for example IP address: 192.168.199.1 Subnet mask: 255.255.255.0. No other settings are required. Click Ok and close all the parent windows.

    Add the new nic to the Hyper-V machine via the settings for the VM, Add Hardware->Network Adapter-Add. Select the 'Static Switch' and click OK.

    Best Regards,

    Ian Xue

    If the Answer is helpful, please click "Accept Answer" and upvote it.

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  2. Ian Xue 39,471 Reputation points Microsoft Vendor
    2025-02-19T07:59:21.38+00:00

    Hi Krasimir Rangelov,

    Thanks for your post. Please understand that there is limited resource for Hyper-V known issue in Windows server 2025. 

    For testing purposes, please add an additional Internal switch via Hyper-V "Virtual Switch Manager" and gave it a name of "Static Switch". Then changed it's settings via Control Panel->Network and Internet->Network and Sharing Center->Change adapter settings. Right click on the new adapter and select Properties->Internet Protocol Version 4 (TCP/IPv4) and set a static IP that is not currently used on your network, for example IP address: 192.168.199.1 Subnet mask: 255.255.255.0. No other settings are required. Click Ok and close all the parent windows.

    Add the new nic to the Hyper-V machine via the settings for the VM, Add Hardware->Network Adapter-Add. Select the 'Static Switch' and click OK.

    Best Regards,

    Ian Xue

    If the Answer is helpful, please click "Accept Answer" and upvote it.

    0 comments

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