General
What is Google Public NTP?
Google Public NTP is a free, global time service that you can use to synchronize to Google's atomic clocks. It implements the leap smear to smoothly handle leap seconds without disruptions.
Why is Google working on an NTP service?
Timekeeping is important to us, and NTP is by far the most widely used time synchronization protocol. In general, NTP works very well. However, we know that many NTP servers do not correctly announce leap seconds, and that even when they are announced through NTP, many systems do not correctly handle the leap.
Since 2008, we've addressed this problem internally by "smearing" the leap second, stretching out the change across the hours around the leap. This has worked very well. When we launched Google Compute Engine, we started providing smeared time via NTP to customers' virtual machines. Google Public NTP makes this available globally to Internet-connected devices.
Are Googlers using Google Public NTP?
Yes. We use Google Public NTP to set the clocks on our laptops, workstations, routers, and many other devices. It's also used by Google Fiber customers.
Are there any cross-product dependencies with Google Public NTP?
No. Google Public NTP is an independent service.
Do I need a Google Account to use Google Public NTP?
No.
Use and support
How do I use Google Public NTP?
Configure your devices to use either the NTP server time.google.com or the
four servers time1.google.com, time2.google.com, time3.google.com, and
time4.google.com. If you cannot configure multiple servers, time.google.com
will automatically select an appropriate Google server nearby.
We have detailed instructions for many popular operating systems.
I am using another NTP service now. Can I also use Google Public NTP?
We recommend that you do not mix smeared and non-smeared NTP servers. The results during a leap second may be unpredictable.
Is Google Public NTP suitable for all types of Internet-enabled devices?
Yes. Google Public NTP can be used on any device that supports NTP or SNTP versions 3 or 4. If you find any situation where Google Public NTP does not work well, let us know.
In which countries is Google Public NTP available?
It is available to Internet users around the world, though your experience may vary greatly based on your specific location.
Does Google Public NTP work with all ISPs?
Google Public NTP should work with most ISPs, assuming you have access to change your NTP settings.
Do I need to use all four Google Public NTP server names?
No. You can use time.google.com to be directed automatically to a nearby
server.
Does it matter in what order I specify the server names?
No, the order does not matter.
What is the SLA for the service?
We are not providing an SLA for this service at this time.
What are the Terms of Service?
Google Public NTP is covered by the Google API Terms of Service.
I'm running an ISP or enterprise network. Can I redirect all my users to Google Public NTP?
Yes. We can accept traffic from any number of NTP clients. But at this time, Google Public NTP is a service without an SLA.
Can I use Google Public NTP for my commercial project or products?
Yes, subject to our terms of service. Google Public NTP is a service without an SLA; we do not provide any commitments about availability or accuracy.
I run an NTP server for my organization. Can I synchronize it to Google Public NTP?
Yes.
Can I use Google Public NTP from Google Compute Engine instances?
Yes, but you will get better results by using metadata.google.internal
(detailed instructions).
Time service from that virtual server is smeared identically to Google Public
NTP.
Can I use Google Public NTP from virtual machines running at other cloud providers?
Yes.
How can I get support from the Google Public NTP team?
We recommend that you join our Google Groups to get updates from the team and ask any questions you have. If you are encountering a problem and would like to report it, see Reporting issues for procedures.
Technical
Are there more details about the leap smear?
Yes, we have more information here.
How does Google Public NTP use the Leap Indicator (LI) field?
Google Public NTP always sets the LI field to 0, because the leap second is applied on the server side using the smear.
Where are your servers currently located?
Google Public NTP servers are available in several of our data centers in North America, Europe, and Asia.
Does Google Public NTP support IPv6?
Yes.
Does Google Public NTP support Autokey or NTS?
No.
If you are interested in secure time distribution, you may also want to look at Roughtime, an experimental project from the Chrome team. Roughtime is not yet a high-precision time service, but it is an experiment in providing trusted time.
Does Google Public NTP support SNTP clients?
Yes.
Does Google Public NTP support Windows Time clients?
Yes.
Does Google Public NTP support mode 6 or mode 7 control messages?
No, it will not respond to control messages, such as those sent by ntpq or
ntpdc.
Could Google Public NTP be abused for NTP amplification attacks?
No. NTP amplification attacks use NTP control messages. Google Public NTP responds only to client time queries, and sends replies that are similar in size to the request.