Windows Event ID 5120 – Microsoft-Windows-Hyper-V-VmSwitch: Virtual Switch Port Connection Failed

Start by examining the detailed event information and restarting the Hyper-V virtual switch service to resolve temporary connection issues.

1. Open Event Viewer and navigate to Applications and Services Logs → Microsoft → Windows → Hyper-V-VmSwitch → Operational
2. Locate Event ID 5120 and note the virtual machine name, network adapter details, and any error codes
3. Open PowerShell as Administrator and check virtual switch status:

   Get-VMSwitch | Select-Object Name, SwitchType, NetAdapterInterfaceDescription
   Get-VMNetworkAdapter -All | Where-Object {$_.Status -ne 'Ok'}

4. Restart the Hyper-V Virtual Machine Management service:

   Restart-Service vmms -Force
   Restart-Service nvspwmi -Force

5. Verify the virtual switch service is running:

   Get-Service vmms, nvspwmi | Select-Object Name, Status

6. Attempt to start the affected virtual machine and monitor for recurring Event ID 5120

Remove and recreate the problematic virtual switch to resolve configuration corruption issues.

1. Document current virtual switch settings:

   Get-VMSwitch | Export-Csv -Path C:\temp\vmswitch-backup.csv -NoTypeInformation
   Get-VMNetworkAdapter -All | Export-Csv -Path C:\temp\vmnetadapter-backup.csv -NoTypeInformation

2. Stop all virtual machines connected to the problematic switch:

   $SwitchName = "YourSwitchName"
   Get-VM | Where-Object {(Get-VMNetworkAdapter -VM $_).SwitchName -eq $SwitchName} | Stop-VM -Force

3. Remove the existing virtual switch:

   Remove-VMSwitch -Name $SwitchName -Force

4. Recreate the virtual switch with the same configuration:

   # For External Switch
   New-VMSwitch -Name $SwitchName -NetAdapterName "Ethernet" -AllowManagementOS $true
   
   # For Internal Switch
   New-VMSwitch -Name $SwitchName -SwitchType Internal

5. Reconnect virtual machines to the new switch:

   Get-VM | Get-VMNetworkAdapter | Connect-VMNetworkAdapter -SwitchName $SwitchName

6. Start the virtual machines and verify network connectivity

Update network adapter drivers and Hyper-V integration services to resolve compatibility issues causing virtual switch failures.

1. Check current driver versions:

   Get-NetAdapter | Select-Object Name, InterfaceDescription, DriverVersion, DriverDate
   Get-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V

2. Open Device Manager and expand Network adapters
3. Right-click the physical network adapter and select Update driver
4. Download the latest drivers from the manufacturer's website or use Windows Update
5. Update Hyper-V integration services on all virtual machines:

   Get-VM | Where-Object {$_.State -eq 'Running'} | ForEach-Object {
       Update-VMIntegrationService -VM $_ -Name "Guest Service Interface"
   }

6. Check for Windows updates that include Hyper-V improvements:

   Get-WindowsUpdate -MicrosoftUpdate | Where-Object {$_.Title -like "*Hyper-V*"}

7. Restart the Hyper-V host after driver updates
8. Verify virtual switch functionality:

   Test-NetConnection -ComputerName "VMName" -Port 3389

Investigate system resource constraints that may prevent successful virtual switch port allocation.

1. Check system memory usage and virtual switch resource consumption:

   Get-Counter "\Memory\Available MBytes", "\Processor(_Total)\% Processor Time"
   Get-Counter "\Hyper-V Virtual Switch(*)\*"

2. Examine Hyper-V host resource allocation:

   Get-VMHost | Select-Object LogicalProcessorCount, MemoryCapacity, VirtualMachineMigrationEnabled
   Get-VM | Measure-Object -Property MemoryAssigned -Sum

3. Monitor virtual switch performance during VM startup:

   $Counters = @(
       "\Hyper-V Virtual Switch(*)\Packets/sec",
       "\Hyper-V Virtual Switch(*)\Bytes/sec"
   )
   Get-Counter -Counter $Counters -SampleInterval 5 -MaxSamples 10

4. Check for memory pressure indicators:

   Get-WinEvent -FilterHashtable @{LogName='System'; Id=2004,2019,2020} -MaxEvents 50

5. Verify network adapter buffer settings in registry:

   $AdapterPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Class\{4d36e972-e325-11ce-bfc1-08002be10318}"
   Get-ChildItem $AdapterPath | ForEach-Object {
       Get-ItemProperty $_.PSPath | Select-Object DriverDesc, *Buffer*
   }

6. Increase virtual switch buffer sizes if necessary and restart the host

Perform deep-level troubleshooting using registry analysis and WMI queries to identify underlying virtual switch database corruption.

1. Export Hyper-V virtual switch registry settings for analysis:

   $RegPath = "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\VirtualSwitch"
   Reg export "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization" C:\temp\hyperv-reg-backup.reg

2. Query WMI for virtual switch configuration details:

   Get-WmiObject -Namespace "root\virtualization\v2" -Class Msvm_VirtualEthernetSwitch | Select-Object ElementName, EnabledState, HealthState
   Get-WmiObject -Namespace "root\virtualization\v2" -Class Msvm_EthernetPortAllocationSettingData

3. Check for orphaned virtual switch ports:

   $AllPorts = Get-WmiObject -Namespace "root\virtualization\v2" -Class Msvm_EthernetSwitchPort
   $AllPorts | Where-Object {$_.ElementName -eq ""} | Select-Object Name, ElementName

4. Validate virtual switch database integrity:

   $VSwitchService = Get-WmiObject -Namespace "root\virtualization\v2" -Class Msvm_VirtualEthernetSwitchManagementService
   $VSwitchService.ValidateVirtualSystemConfiguration()

5. Reset virtual switch WMI namespace if corruption is detected:

   Stop-Service vmms -Force
   winmgmt /resetrepository
   Start-Service vmms

6. Recreate virtual switch configuration from backup:

   Import-Csv C:\temp\vmswitch-backup.csv | ForEach-Object {
       New-VMSwitch -Name $_.Name -NetAdapterName $_.NetAdapterInterfaceDescription
   }