about difference the public time server , time.microsoft.com , and Microsoft time server

Question

I investigate a time server in azure service.

please confirm my understanding .

・in using Asure VM service, the host machine syncronize "Windows time server", and a virtual machine syncronze "time.windows.com" , the public time server of Windows .

・"Windows time server" and "time.windows.com" are differet, and when a system connects to internet, the virtual machine can syncronize "time.windows.com".

In private network, be not able to do that.

・Directly, we can't connect to "Windows time server" which the host machine syncronize , from a virtual machine.

Answer 1

Hello, @ryo shinba !

My understanding is that on Azure virtual machines (VMs), the VM synchronizes with "Windows Time Server" and "time.windows.com". Is that correct?

Azure hosts are synchronized to internal Microsoft time servers that take their time from Microsoft-owned Stratum 1 devices, with GPS antennas. Virtual machines in Azure can either depend on their host to pass the accurate time (host time) on to the VM or the VM can directly get time from a time server, or a combination of both.

On a Windows VM, that leaves you with the following three configuration options:

• Host time and time.windows.com. This is the default configuration used in Azure Marketplace images.
• Host-only.
• Use another, external time server with or without using host time. For this option follow the Time mechanism for Active Directory Windows Virtual Machines in Azure guide.

This means that the VM synchronizes with the host time, time.windows.com, and/or another, external time server.

Read more:

• Time sync for Windows VMs in Azure
• Time sync for Linux VMs in Azure

"Host time" and "time.windows.com" are different, and when a VM is connected to the internet it can synchronize with "time.windows.com". Is that correct?

Host time and time.windows.com are different. Host time is based on internal Microsoft time servers and time.windows.com would need a network connection.

Read more:

• How the Windows Time Service Works

What about private networks?

You can rely on internal host time from Azure, or make exceptions for time.windows.com or another external time service.

I hope this helps!