Hyper V Time Synchronization on a Windows Based Network

A very common query that I get asked to help out with in relation to Hyper-V installations is the small (but very important!) task of getting time synchronization working between the physical environment and the virtual environment.

There are a lot of blog posts out there at the moment covering this topic but I thought I'd throw my 2 Cents in based on the solution that works for me.

Background

 

Firstly, I need to explain a little about how time synchronization works in a domain environment.

When you install the first domain controller in your domain, this DC is the owner by default of all 5 FSMO roles within Active Directory. The PDC Emulator Role is the one that is responsible for Active Directory Time Synchronization.

When you add member servers or client computers to your new domain, they then default to using the PDC Emulator Role holder as their time synchronization source. If you move the PDC Emulator Role to another Domain Controller, then this will become the time synchronization source for that domain in place of the original DC.

When you install a Member Server into Active Directory and add the Hyper-V role onto that member server things start getting a little bit more interesting!

The physical Hyper-V host that is now a member server in your new domain will use the PDC Emulator Role holder as its time synchronization source as you would expect it to, however, when you add virtual machines to that Hyper-V host and the 'Hyper-V Integration Services' are installed onto each virtual machine, then that VM starts to synchronize its time from the Hyper-V host it is based on and not from the PDC Emulator Role!

This 'VM to Host' time sync generally isn't a problem when all of your domain controllers are physical machines as the Hyper-V host updates itself from a physical machine separate from the virtual environment and this keeps the internal VM's up to date.

What happens though when your PDC Emulator Role holder Domain Controller (gasp for air!) is based on the Hyper-V host as a virtual machine? You guessed it - time sync issues occur and the virtual DC's clock starts to move out away from the time on the Hyper-V host, which in turn then knocks the rest of the domain off-skew as they are- as mentioned above, configured by default to sync from the PDC Emulator Role Holder.

The Wrong Way

 

A lot of people - including myself for a long time - took the stance that to resolve this problem, the best and easiest solution was to just remove the 'Time Synchronization' tick box from the 'Integration Components Offered' section on the virtual Domain Controller that holds the PDC Emulator Role. Once this step was completed and the time within the virtual DC was configured correctly, this nearly always resolved the time sync issues on site. I use the word 'nearly' in that sentence though as this workaround didn't always work.

The Right Way

 

So what's the solution? A couple of months ago, I came across a blog post from Ben Armstrong -Virtualization Program Manager at Microsoft -covering this subject and specifically around the Hyper-V 'Time Synchronization Integration Service'. In this post, Ben states categorically that you SHOULD NOT disable the 'Time Synchronization Integration Service' on any virtual machine within Hyper-V and instead you should manipulate the Windows Time Service (w32tm service) from within the virtual DC to get the results that you need for a coherent time sync within your domain!

The link to Ben Armstrong's blog post is as follows:

http://blogs.msdn.com/b/virtual_pc_guy/archive/2010/11/19/time-synchronization-in-hyper-v.aspx

To summarise his post and outline my steps when faced with time sync issues in a Hyper-V environment, I carry out the following procedure on all my VM's (most importantly, my virtual DC's):

 

 

Enable all of the Hyper-V Integration Services (see below)

Check each virtual domain controller's time source using the "w32tm /query /source" command

If the virtual DC is using the 'VM IC Time Synchronization Provider', you need to type the following commands into the command line within the virtual DC to leave the Hyper-V time sync enabled for VM reboots but not for when the VM is up and running:

reg add HKLM\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\VMICTimeProvider /v Enabled /t reg_dword /d 0

(Select 'Yes' if requested after you enter this command)

w32tm /config /syncfromflags:DOMHIER /update

(This command tells the virtual DC to sync from within the Domain)

net stop w32time & net start w32time

(This command stops and then restarts the Windows Time Service)

w32tm /resync /force

(This command queries the Windows Time Synchronization Service again and should now detail the internal time server - hopefully the DC with the PDC Emulator Role)

At this point, your Virtual Domain Controller should use itself for time sync when it is online and it will use the Hyper-V host for when it is rebooting or coming out of a 'Saved State' and before the Windows O/S loads

Finally, all that is left to do now is to configure the Virtual Domain Controller and each Hyper-V host that you have in your domain to synchronize with an external time source provider (NTP Provider)

Note: Make sure to follow the instructions in this next paragraph exactly as you read them as clicking on the 'Internal Time Source' option will not give you the desired result!

 

Use this link from Microsoft to automatically configure an external authoritative time source by selecting the 'Microsoft Fix It' button half way down the page under the 'Configure the Windows Time Service to use an External Time Source':

http://support.microsoft.com/kb/816042

The 'Microsoft Fix It' button should initiate a wizard that will prompt you to enter your external NTP servers (you can enter two in here for redundancy) and will then configure the registry to reflect these changes automatically.

 As I'm based in Ireland, the NTP provider that I prefer to use is  - ie.pool.ntp.org


Hopefully this will help you to get a better handle on Time Sync in a Hyper-V environment.