The NTP Pool project is a pool of publicly available time servers, all volunteers. Time servers in the pool are usually stratum 1 or 2 servers. Although the pool consists of NTP servers worldwide, it is divided into geographical location so users can pick from a pool of time servers closest near their geographical position. The pool is probably the most used pool of NTP servers.
Using servers from the pool uses DNS load balancing to randomly assign one or more servers to synchronize to. Up to four different servers can be used. To avoid DNS caching from taking the same server more than once, additional DNS records have been created in the form of:
It is recommended to use the pool to select servers rather than choosing fixed servers. This ensures that if a server ever becomes unreachable, another server will automatically be selected from the pool. Because selection occurs only at startup of the time service on your server, it is also highly recommended to select at least two servers from the pool to quickly ensure a failback if the first server goes down.
If my server is in Europe, and I want to pick two randomly selected servers from the European pool of time servers, I would set the peers on my server to:
More information about usage can be found on the website: http://www.pool.ntp.org/use.html.
If you wish, you can also join the pool to allow other users to use your publicly available time server. NTP only uses a very limited amount of bandwidth and server resources, and is very safe when configured properly.
More information about joining can be found on the website: http://www.pool.ntp.org/join.html.