Untagged VLAN - Server 2025 Hyper-V

Hi,

I have a strage issue and not finding a solution.

Using Server 2025 with two node Hyper-V cluster. Most of the machines using VLANs which works fine.

Some machines using no VLAN config. Which usually means the "Access VLAN 1" regarding our switch configuration.

With Server 2019 this worked fine.

With Server 2025 same NIC port, same server/NIC hardware "Untagged" VMs don't get any network connection. If I add a second NIC to the VM "Untagged" the NIC get immidiatly an IP address and has a proper connection. If I remove the first NIC, the second NIC stop working.

It looks like something has changed with Server 2025 (maybe already with Server 2022). Do you have any idea what kinde of problem I have found?

Thanks

Jack