Skip to main content

Google's public NTP servers?

I was struggling with finding a good set of low-ping NTP servers for use as upstream sources in the office. Using pool.ntp.org is great and all, but the rotating DNS entries aren't fabulous for Windows NTP clients (or really any NTP software except the reference ntpd implementation).

ntpd resolves a server hostname to an IP once at startup, and then sticks with that IP forever. Most other NTP clients honor DNS TTLs, and will follow the rotation of addresses returned by pool.ntp.org. This means Windows NTP client using the built-in Windows Time Service will actually be trying to sync to a moving set of target servers when pointed at a pool.ntp.org source. Fine for most client, but not great for servers trying to maintain stable timing for security and logging purposes.

I stumbled across this link referencing Google's ntp servers at hostname time[1-4].google.com. These servers support IPv4 and IPv6, and seem to be anycast just like Google's public DNS servers at 8.8.8.8. time4.google.com is only few milliseconds away from some widely dispersed servers to which I have access. Indeed, plugging time4.google.com into CA's global ping tool shows that they are clearly "close" in terms of latency to multiple locations globally, which is only possible with anycast routing.

Are these servers truly public like Google Public DNS? They're not publicized by Google, but they seem to work pretty well as an alternative to pool.ntp.org for systems that run NTP software other than ntpd.

Update

Google has since announced their public NTP service  based on their global anycast network, but using different IPs than their public DNS. These NTP servers implement leap second smearing.

Comments

Popular posts from this blog

Fixing slow NFS performance between VMware and Windows 2008 R2

I've seen hundreds of reports of slow NFS performance between VMware ESX/ESXi and Windows Server 2008 (with or without R2) out there on the internet, mixed in with a few reports of it performing fabulously.
We use the storage on our big Windows file servers periodically for one-off dev/test VMware virutal machines, and have  been struggling with this quite a bit recently. It used to be fast. Now it was very slow, like less than 3 MB/s for a copy of a VMDK. It made no sense.
We chased a lot of ideas. Started with the Windows and WMware logs of course, but nothing significant showed up. The Windows Server performance counters showed low CPU utilization and queue depth, low disk queue depth, less than 1 ms average IO service time, and a paltry 30 Mbps network utilization on bonded GbE links.
So where was the bottleneck? I ran across this Microsoft article about slow NFS performance when user name mapping wasn't set up, but it only seemed to apply to Windows 2003. Surely the patch me…

Presets versus quality in x264 encoding

I'm scoping a project that will require re-encoding a large training video library into HTML5 and Flash-compatible formats. As of today, this means using H.264-based video for best compatability and quality (although WebM might become an option in a year or two).
The open source x264 is widely considered the state of the art in H.264 encoders. Given the large amount of source video we need to convert as part of the project, finding the optimal trade-off between encoding speed and quality with x264-based encoders (x264 itself, FFmpeg, MEencoder, HandBrake, etc.) is important.
So I created a 720p video comprised of several popular video test sequences concatenated together. All of these sequences are from lossless original sources, so we are not re-compressing the artifacts of another video codec. The sequences are designed to torture video codecs: scenes include splashing water, flames, slow pans, detailed backgrounds and fast motion. I did several two-pass 2500 kbps encodings using …