Where do stratum 1 NTP servers get time from?

Where do stratum 1 NTP servers get time from?

• Averaging time from other trusted sources
• A stratum 2 clock
• A reference clock
• They generate it internally 

 

EXPLANATION

Stratum 1 NTP servers are the highest, most trusted order of NTP servers. They receive their time by being directly connected to a reference clock, typically an atomic clock. Reference clocks are also referred to as stratum 0 devices.

http://support.ntp.org/bin/view/Servers/ServerStratum