Trunking With Hyper-V Networking

When doing lab work, or real life implementations you’ll need to go beyond the basic 101 stuff to build solutions every now and then. This is especially true when using virtual network appliances. Networking means you’ll you’ll be dealing with Link Aggregation Groups, Trunking, MLAG, routing, LACP … in short the tools of the trade when doing networking. In my experience I use trunking in Hyper-V mostly to mimic real world scenarios where trunking is used (firewall, routers, load balancers). These tend to be limited in usable ports in real life. So even, before you run out of physical ports on your Hyper-V host to work with we leverage them to mimic the real live environment. This leads us to trunking with Hyper-V networking

I for one have used this on 10Gbps ports on bot physical and virtual load balancers in the uplink to the switches. As you can imagine when doing redundant (teaming) cabling with HA load balancers you’re consuming 10Gbps ports and not all VLANs warrant a dedicated 10Gbps uplink, even if you had ‘m.

Trunking & VLAN’s are the way we deal with this in the network hardware world and we can do the same in Hyper-V. In the Hyper-V Manager GUI you will not find a way to define a trunk on an vNIC attached to a vSwitch. But this can be done via PowerShell. So please do not reject Hyper-V as not being up to the job. It is. Let me show you how you can do trunking with Hyper-V networking.

Generally on a clean install I dump the default vNIC. DO NOT DO this blindly on an existing deployed appliance virtual machine.

#Delete the default network adapter
Remove-VMNetworkAdapter -VMName VLM200-1 -Name "Network Adapter"

I then add the number of ethernet ports I need on my Kemptechnologies virual Load Master.

#Create the VLM200 ports (4 like it's physical counterpart)
For ($Count=0; $Count -le 3; $Count ++)
Add-VMNetworkadapter -VMName VLM200-1 -Name "Eth$Count"

A peak at our handy work via Get-VMNetworkAdapter -VMName VLM200-1 shows our 4 ports.


As you can see I like to name my network adapters with a distinctive name. In combination with the switch name it enables me to identify the NICs better. Combine that with a good naming policy inside the VM if possible. In Windows Server 2016 you can hot add and remove vNICs and new “Device Naming”

(see Hot add/remove of network adapters and enabling device naming in Windows Server Hyper-V) functionality which only makes the experience better in relation to uptime and automation.

Now let’s say we use eth0 for management and for the HA heartbeat. That leaves Eth2 and Eth3 for workloads. We could even aggregate these (redundancy, heart beat). In this demo we’ll configure Eth3 as a trunk with a list of allowed VLANs. We keep the native VLAN ID on 0 as it is by default. Only in specific situations where you have changed this in the network should this be changed.

#Trunk Eth3 and add the required VLAnIDs
Set-VMNetworkAdaptervlan -VMName VLM200-1 -VMNetworkAdapterName "Eth3"-Trunk -AllowedVlanIdList "10, 20, 30" -NativeVlanId 0

Which delivers us what we need to get our network appliance going


In your virtual appliance you can now create VLANs on Eth3. How this shows up is dependent on the appliance. In this example a Kemp Virtual Load Master. Here we mimic a 4 port load master. We’re not doing trunking because we ran out of the max supported number of NICs we can add to a virtual machine.


A word of warning. You will not see this configuration in the settings via the GUI.
Manipulating the VLAN settings in the GUI will overwrite the settings without a warning.
So be careful with configuration of your virtual network appliance(s).  As an example I’ll touch the VLAN setting of Eth3 and give it VLAN 500.


We now have a look at our VLAN settings of the appliance


That vNIC is now in Access mode with VLAN 500. Ouch, that will seriously ruin your day in production! Be careful!

On top of this some appliances do not respond well to such misconfigurations on the switch side (both physical and virtual switches). This leads not only to service interruption but could lead to the inability to mange the appliance, requiring a reboot of them etc.

Anyway, so yes you can do trunking with Hyper-V networking on a vNIC but this normally only makes sense I you have an appliance running that knows what to do with a trunk such as a virtual  firewall, router or load balancer.

Virtual Network Appliances I Use for Hyper-V Labs

When you build and maintain a test lab you’re always on the lookout for gear you can use. That’s either hardware or virtual appliances. My main concern is cost, it should work well on Hyper-V and the ability to mimic real world environments. That’s a great help for educational purposes as well as for testing and as an aid to troubles shooting. One of the nice things virtualization and now also cloud IAAS offers is the ability to run virtual storage and network appliances that allow us to have that real world look and feel. Add to that ever more software defined storage, networking and compute and we’re able to build very realistic labs. The limits we’re left with are time, money and space.

When building a lab some people tend to run into perceived limitations of their hypervisor. That’s to be expected as for many that hypervisor is just something to quickly get up and running an get to work writing code, implementing a backup solution or whatever the workload at hand is all about. The tip here is not to give up to fast.

More recently I’m build/working on a new lab setup simulating different sites. I need to route between these isolated test networks and load balance traffic in a site redundant manner. The idea was to mimic real life as well as we good. Add to that lab setup an Azure “site” and it’s fun all over. It’s all based on Hyper-V and Windows Server virtual machines but some components are not. Windows NLB has had its best day and RRAS is limited in the abilities I need to test. They can and do work fine for certain scenarios, but not for all that I need to test. I add virtual load balancers, virtual switches with the look and feel of physical ones and the same for virtual firewalls.

Now in real life you’ll be dealing with Link Aggregation Groups, Trunking, MLAG, routing, teaming … in short the tools of the trade when doing networking. One side effect of this is that on a Hyper-V host you quickly run out of physical network ports to work with. That’s not a problem, in real life your firewall or load balancer does not have 48 ports either. Often you have 4 to 8 and sometimes more, but often not, ports at your disposal and depending on the complexity that’s more than enough or not at all. Trunking & VLAN’s are the way we deal with this. In the Hyper-V GUI you will not find a way to define a trunk on an vNIC attached to a vSwitch. But this can be done via PowerShell. So please do not reject Hyper-V as not being up to the job. It is! Read about this in my blog post.

People often ask me what virtual network appliances I Use for Hyper-V Labs. This does vary over time, but there are some constants. In the lab I hate wasting time on time bombed trials. So I avoid those in favor of either fully featured solutions or I use free open source alternatives. Smart vendors provide the easiest access possible to their solutions. They realize that easy access delivers the ability to learn and test every aspect of the products which make a huge difference in the success of their offerings in the real world. When it comes to load balancers I use the KEMP Virtual Load Masters. You can read more about these in projects and lab testing  in blogs about the KEMP (Virtual) Load Master.

As an MVP I got 1 free license. Together with the ability to restore configurations I can have a pseudo permanent redundant load balancing setup. Only building labs for multi-site geo load balancing solutions requires to start from scratch every time. For routing I use VyOS, it works on both hardware and on a bunch of hypervisors with X64 bit virtual machines. When I need the look and feel of a firewall you’ll encounter in business I use Opnsense. It supports the synthetic vNICs with the enlightened Hyper-V drivers. Yup, the integration components are there.  It doesn’t boot from UEFI so no Generation 2 virtual machine support as of yet. imageimage

Another good one is IPFire. This one also does a nice job with the integration components.


I also have a DELL SonicWall in my home office where I have some ports to play with but it tends to be leveraged more for the permanent parts of the lab. It’s a crucial & permanent component.

SonicWALL NSA 220 Wireless-N Appliance

Find All Virtual Machines With A Duplicate Static MAC Address On A Hyper-V Cluster With PowerShell

During some trouble shooting recently I needed to find all virtual machines with a duplicate static MAC address on a Hyper-V cluster with PowerShell. I didn’t feel like doing this via the GUI for obvious reasons. I needed this because while trying to find the reason why a VM lost connectivity to one of it two NICs I discovered it had a static MAC address. No one had a good reason for this VM to have a static MAC address I stopped the VM, switched that NIC to a dynamic MAC address and rebooted. All was well afterwards

But I still needed to find out what potentially caused the issue, my guess was a duplicate MAC address (what else?). The biggest candidates for having a duplicate MAC was another VM or VMs. So here’ s some PowerShell that will list all clustered VMs that have a static MAC address.

Get-ClusterGroup | ? {$_.GroupType -eq 'VirtualMachine'} `
| get-VM | Get-VMNetworkAdapter | where-object {$_.DynamicMacAddressEnabled -eq $False}

Let’s elaborate the code a bit and search for the occurrence of duplicates in MAC address

$AllNicsWithStaticMAC = Get-ClusterGroup | ? {$_.GroupType -eq 'VirtualMachine'} `
| get-VM | Get-VMNetworkAdapter | where-object {$_.DynamicMacAddressEnabled -eq $False}

$AllNicsWithStaticMAC.GetEnumerator() | Group-Object MacAddress | ? {$_.Count -gt 1} | ft * -autosize

The result is as follows


So in our lab simulation we have found a static MAC address that occurs 3 time!

If you have 200 VMs running on that cluster you might not want to look over the list manually, not that I’m hoping you have 200 VMs with the same MAC address, but just to find the servers that have the same MAC address fast. For this we adapt the above PowerShell a bit

$AllNicsWithStaticMAC = Get-ClusterGroup | ? {$_.GroupType -eq 'VirtualMachine'} `
| get-VM | Get-VMNetworkAdapter | where-object {$_.DynamicMacAddressEnabled -eq $False}

$AllNicsWithStaticMAC.GetEnumerator() | Group-Object MacAddress | ? {$_.Count -gt 1} | ft * -autosize

if($AllNicsWithStaticMAC -ne $null)
    (($AllNicsWithStaticMAC).GetEnumerator() | Group-Object MacAddress `
    | ? {$_.Count -gt 1}).Group | Ft MacAddress,Name,VMName -GroupBy MaCAddress -AutoSize
    "No Static MAC addresses where found on your cluster"

Which results in a nice list of the duplicate MAC address, on what Network adapter is sits an on what virtual machine. It sorts by (duplicate) MAC address, Network Adapter Name and VMName.


The lab demo is a bit fabricated as I’m not creating duplicate MAC address for this blog on my lab clusters.

I hope this helps some of you when you need to find all virtual machines with a duplicate static MAC address on a Hyper-V cluster with PowerShell. Now you can adapt the code to only look for dynamic duplicate MAC addresses or both static and dynamic MAC addresses. You get the gest. Thank your for reading.

Recover From Expanding VHD or VDHX Files On VMs With Checkpoints

So you’ve expanded the virtual disk (VHD/VHDX) of a virtual machine that has checkpoints (or snapshots as they used to be called) on it. Did you forget about them?  Did you really leave them lingering around for that long?  Bad practice and not supported (we don’t have production snapshots yet, that’s for Windows Server 2016). Anyway your virtual machine won’t boot. Depending on the importance of that VM you might be chewed out big time or ridiculed. But what if you don’t have a restore that works? Suddenly it’s might have become a resume generating event.

All does not have to be lost. Their might be hope if you didn’t panic and made even more bad decisions. Please, if you’re unsure what to do, call an expert, a real one, or at least some one who knows real experts. It also helps if you have spare disk space, the fast sort if possible and a Hyper-V node where you can work without risk. We’ll walk you through the scenarios for both a VHDX and a VHD.

How did you get into this pickle?

If you go to the Edit Virtual Hard Disk Wizard via the VM settings it won’t allow for that if the VM has checkpoints, whether the VM is online or not.


VHDs cannot be expanded on line. If the VM had checkpoints it must have been shut down when you expanded the VHD. If you went to the Edit Disk tool in Hyper-V Manager directly to open up the disk you don’t get a warning. It’s treated as a virtual disk that’s not in use. Same deal if you do it in PowerShell

Resize-VHD -Path “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd” -SizeBytes 15GB

That just works.

VHDXs can be expanded on online if they’re attached to a vSCSI controller. But if the VM has checkpoints it will not allow for expanding.


So yes, you deliberately shut it down to be able to do it with the the Edit Disk tool in Hyper-V Manager. I know, the warning message was not specific enough but consider this. The Edit disk tool when launched directly has no idea of what the disk you’re opening is used for, only if it’s online / locked.

Anyway the result is the same for the VM whether it was a VHD or a VHDX. An error when you start it up.

[Window Title]
Hyper-V Manager

[Main Instruction]
An error occurred while attempting to start the selected virtual machine(s).

‘DidierTest06’ failed to start.

Synthetic SCSI Controller (Instance ID 92ABA591-75A7-47B3-A078-050E757B769A): Failed to Power on with Error ‘The chain of virtual hard disks is corrupted. There is a mismatch in the virtual sizes of the parent virtual hard disk and differencing disk.’.

Virtual disk ‘C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD_8DFF476F-7A41-4E4D-B41F-C639478E3537.avhd’ failed to open because a problem occurred when attempting to open a virtual disk in the differencing chain, ‘C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd’: ‘The size of the virtual hard disk is not valid.’.


You might want to delete the checkpoint but the merge will only succeed for the virtual disk that have not been expanded.  You actually don’t need to do this now, it’s better if you don’t, it saves you some stress and extra work. You could remove the expanded virtual disks from the VM. It will boot but in many cased the missing data on those disks are very bad news. But al least you’ve proven the root cause of your problems.

If you inspect the AVVHD/AVHDX file you’ll get an error that states

The differencing virtual disk chain is broken. Please reconnect the child to the correct parent virtual hard disk.


However attempting to do so will fail in this case.

Failed to set new parent for the virtual disk.

The Hyper-V Virtual Machine Management service encountered an unexpected error: The chain of virtual hard disks is corrupted. There is a mismatch in the virtual sizes of the parent virtual hard disk and differencing disk. (0xC03A0017).


Is there a fix?

Let’s say you don’t have a backup (shame on you). So now what? Make copies of the VHDX/AVHDX or VHD/AVHD and save guard those. You can also work on copies or on the original files.I’ll just the originals as this blog post is already way too long. If you. Note that some extra disk space and speed come in very handy now. You might even copy them of to a lab server. Takes more time but at least you’re not working on a production host than.

Working on the original virtual disk files (VHD/AVHD and / or VHDX/AVHDX)

If you know the original size of the VHDX before you expanded it you can shrink it to exactly that. If you don’t there’s PowerShell to the rescue if you want to find out the minimum size.


But even better you can shrink it to it’s minimum size, it’s a parameter!

Resize-VHD -Path “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd” -ToMinimumSize

Now you not home yet. If you restart the VM right now it will fail … with the following error:

‘DidierTest06’ failed to start. (Virtual machine ID 7A54E4DB-7CCB-42A6-8917-50A05354634F)

‘DidierTest06’ Synthetic SCSI Controller (Instance ID 92ABA591-75A7-47B3-A078-050E757B769A): Failed to Power on with Error ‘The chain of virtual hard disks is corrupted. There is a mismatch in the identifiers of the parent virtual hard disk and differencing disk.’ (0xC03A000E). (Virtual machine ID 7A54E4DB-7CCB-42A6-8917-50A05354634F)


What you need to do is reconnect the AVHDX to it’s parent and choose to ignore the ID mismatch. You can do this via Edit Disk in Hyper-V Manager of in PowerShell. For more information on manually merging & repairing checkpoints see my blogs on this subject here. In this post I’ll just show the screenshots as walk through.






Once that’s done you’re VHDX is good to go.

For a VHD you can’t shrink that with the inbox tools. There is however a free command line tool that can do that names VHDTool.exe. The original is hard to find on the web so here is the installer if you need it. You only need the executable, which is portable actually, don’t install this on a production server. It has a repair switch to deal with just this occurrence!

Here’s an example of my lab …

D:\SysAdmin>VhdTool.exe /repair “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd” “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD_8DFF476F-7A41-4E4D-B41F-C639478E3537.avhd”


That’s it for the VHD …

You’re back in business!  All that’s left to do is get rid of the checkpoints. So you delete them. If you wanted to apply them an get rid of the delta, you could have just removed the disks, re-added the VHD/VHDX and be done with it actually. But in most of these scenarios you want to keep the delta as you most probably didn’t even realize you still had checkpoints around. Zero data loss Winking smile.


Save your self the stress, hassle and possibly expense of hiring an expert.  How? Please do not expand a VHD or VHDX of a virtual machine that has checkpoints. It will cause boot issues with the expanded virtual disk or disks! You will be in a stressful, painful pickle where you might not get out of if you make the wrong decisions and choices!

As a closing note, you must have have backups and restores that you have tested. Do not rely on your smarts and creativity or that others, let alone luck. Luck runs out. Otions run out. Even for the best and luckiest of us. VEEAM has save my proverbial behind a few times already.