I wanted to use in my test environment an NTP server on Microsoft Windows Server 2008 R2 that would function as a syncing point for my Cisco routers and switches. The starting issue is that Cisco devices will not sync with Windows integrated NTP server and the reason is that Windows use SNTP as network time protocol.
SNTP basically provides the same features as NTP, but uses a simpler algorithm to calculate the difference in time between the two network devices. Because of this algorithm, SNTP is less accurate than NTP where on the other side it uses fewer system resources. It is better and recommended to use SNTP on i.e. mobile devices and some consumer level apps where time can be a little off. In our case it is also recommended to use a full NTP:)
We will use a very nice 3rd party NTP software that runs on top of Windows called Meinberg NTP. You can find and read about it on their web page HERE.
As a Windows version we will use Microsoft Windows Server 2008 R2 edition and email@example.com executable as NTP server app.
Now the installation process will begin and after it has finished we will be asked about the configuration settings. You can define predefined public NTP servers according to your location. We choose none but specified two NTP servers, as we also marked “ON” the “Add local clock as a last…”. This will make the system inbuilt clock to act as a NTP server in case the NTP servers on the Internet are not available.
From the Start Menu choose Quick NTP status that is located in the Meinberg start menu folder to verify the status of your NTP server and its synchronization. There are also available many other options as start/stop/restart the NTP service but that you will find best explained in the Meinberg documentation.
After you have verified that the server is up and running, all that is left is the Cisco NTP configuration. That configuration is pretty simple but there are also many little things that you have to be aware of.
Here is a sample of NTP configuration on the 12.2 (52) SE IOS:
ntp source Loopback30
ntp server 10.56.11.245
“show ntp status”
“show ntp association”
“show ntp association detail”
Use the “debug ntp packet” command to view the NTP packets that are generated by the router.
Hope it helped!