Stratum 1 NTP servers get their time data from the reference clock. Stratum 2 NTP servers synchronize with Stratum 1 servers. You can have up to 15 levels. For a list of public Stratum 1 and 2 servers see www.eecis.udel.edu/~mills/ntp/servers.html. Be sure to read and honor the access policy of the public NTP servers you use.
NTP servers and NTP clients get time data from Stratum 1 servers, though in practice, NTP clients shouldn't do so because thousands of individual client requests would place too much of a burden on a Stratum 1 server. It's best to set up a local NTP server that your clients use for time services.
The NTP hierarchy is fault-tolerant and redundant. In the diagram below, two Stratum 2 NTP servers are synchronizing to six different Stratum 1 servers, each going over independent paths. The internal hosts are synchronizing with the internal NTP servers. The two Stratum 2 NTP servers coordinate time between themselves. If a path to a Stratum 1 server fails or a Stratum 2 server fails, the redundant Stratum 2 server continues the synchronization process.
Likewise, Stratum 3 hosts and devices can use either of the Stratum 2 NTP servers. More important, using a redundant network of NTP servers ensures that time servers are always available. By synchronizing with multiple time servers, NTP uses the data from all the sources to calculate the most accurate time.
NTP doesn't actually set time. It adjusts the local clock using a time offset, which is the difference between the NTP server's time and the local clock. NTP servers and clients update their times by adjusting the local clock to the current time gradually or all at once.
Discover the benefits of scalable backbone and network services for application and cloud providers.
Network automation is gaining momentum. Here's how you can drive this powerful technology to its full potential.
Subsea cable alternatives can provide a level of comfort for those concerned about disruptions. Realistically, they will continue to play a small, but critical role in the short term.
