Set Your Clocks With Pooled NTP Servers

flok writes "Since we all want to have the time correctly set on our servers we all want to synchronize to some ntp-server. Not everyone has such an NTP server available, so that is why www.pool.ntp.org was started. If your server is synced to some discrete timesource like GPS or something like that you can also join the group to help this initiative!"

Comments

Many publicly available time servers

[Visigothe]

There are many publicly available time servers. I don't quite get why this is all that important. When "Public Time Server" is entered in Google, the first hit yields a good resource:

http://www.eecis.udel.edu/~mills/ntp/servers.html

Can anyone enlighten me on why this is special? I couldn't make it out from the site

Re:Many publicly available time servers

[Anonymous Coward]

There are many publicly available time servers. I don't quite get why this is all that important.

It's useful to use the pool as a default address when distributing software, routers, etc., to avoid situations like this: Flawed Routers Flood University of Wisconsin Internet Time Server.

Re:Many publicly available time servers

[rusty0101]

Yep, the protocol is "low bandwidth", then again that does nothing for the utilization bandwidth that the server's experience.

By default, Windows 2k (and beyond) when time service is started all hit Microsoft's time server. Can't think of a better way to burn up Microsoft's bandwidth myself, but such is life.

By default Netgear routers (up until the last six months or so) all attemmpted to get their time reference from the University of Wisconsin't time server. There was a flaw in the software that caused the implementation that caused the devices to pull down time samples repeatedly, and this caused an effective denial of service to the UW connectivity for the location that provided that clock service. (perhaps a fix would have been to alter the dns entry to point back to microsoft's server, though that might have been actionable.)

Additionally just because a time server is available today, does not mean that it will be publically available tomorrow.

Personally I like the option of using Tick and Tock, over using a gps time source, because Tick and Tock have been corrected for cosmic clock drift, while the gps clocks have not been so adjusted.

But that's just me. Use your own adjusted time source.

-Rusty

Re:Many publicly available time servers

[Anonymous Coward]

Can anyone enlighten me on why this is special? I couldn't make it out from the site

I didn't take me much to figure it out. Public time servers have always been a pain. Some are up and down. Many require you send a nice e-mail before using them. This is much easier. You just add "server pool.ntp.org" three times. Each time it gets the IP of a different server, so you have redundancy and easy configuration for free.

I wish someone had thought of that before. Now, the important thing, is someone monitoring the pool and tossing out bad servers? It says there was a discussion on the e-mail list, but I've got better things to do now.

Use .pool.ntp.org instead...

[SchnauzerGuy]

As pool.ntp.org will assign you timeservers from all over the world, time quality will not be ideal. You get a bit better result if you use the continental zones (europe, north-america, oceania and asia.pool.ntp.org currently exist), and even better time if you use the country zone (like ch.pool.ntp.org in Switzerland). Note, however, that the country zone might not exist for your country, or might contain only one or two timeservers. If you know timeservers that are really close to you (measured by network distance, with traceroute or ping), time probably will be even better.

You will definitely want to use either the continent or country code versions of pool.ntp.org, otherwise you might end up sychronizing with a very distant timeserver, resulting in more NTP jitter and less accurate time.

For example, us.pool.ntp.org or north-america.pool.ntp.org would be a good choice for people in the United States.

Re:time.apple.com

[Twirlip of the Mists]

I remember hearing a few years ago that the folks who ran tick and tock asked that only second-tier time servers sync to them, and that all the "leaf nodes" sync to a second-tier server. That's why I don't use tick or tock any more.

Re:Accuracy vs Precision

[mgarraha]

I would try something like this for a local server, e.g. 192.168.1.42:

server us.pool.ntp.org
server us.pool.ntp.org
server us.pool.ntp.org
driftfile /etc/ntp/drift
restrict default nomodify notrap noquery
restrict 127.0.0.1
restrict 192.168.0.0 mask 255.255.0.0 notrust nomodify notrap

Everything else would be a client, like this:

server 192.168.1.42
driftfile /etc/ntp/drift
restrict default ignore
restrict 127.0.0.1
restrict 192.168.1.42 nomodify notrap noquery

Re:NIST?

[arcade]

Uhm. It's a stratum 1 server. That is what is wrong. You should never abuse stratum 1 servers unless you're a selfish bastard.

Unless you want time to get really unreliable, you should use stratum 2 or stratum 3 servers, as the stratum 1 servers cannot keep up if everybody uses them.

Personally I sync my local stratum 3 timeserver against two stratum two servers -- and about 50 computers sync against my one stratum 3 server.