Which statement about NTP Stratum Levels is true?

Which statement about NTP Stratum Levels is true?

• A. Stratum-0 servers are used on the network; they are not directly connected to computers which then operate as stratum-1 servers
• B. Stratum-1 time server is linked over a network path to a reliable source of UTC time such as GPS, WWV, or CDMA transmissions
• C. A stratum-3 server gets its time over a network link, via NTP, from a stratum-2 server, and so on
• D. A stratum-2 server is directly linked (not over a network path) to a reliable source of UTC time such as GPS, WWV, or CDMA transmissions

Answer: (C)

In NTP, time is distributed in a hierarchy that starts with a reference clock (such as GPS, WWV, or CDMA) which is considered the stratum-0 source. A server that is directly connected to that reference clock becomes a stratum-1 server. Stratum-2 servers obtain their time from one or more stratum-1 servers over the network, and stratum-3 servers obtain theirs from stratum-2 servers, again over the network, continuing outward with each hop adding one to the stratum level. So a stratum-3 server getting its time via an NTP network path from a stratum-2 server is exactly how the hierarchy is designed to propagate time. The other statements don’t fit how NTP levels are structured. Stratum-0 devices aren’t servers on the network; they’re the reference clocks that feed stratum-1. A stratum-1 server is connected directly to that reference clock, not via a network path to the clock itself. Stratum-2 servers aren’t directly linked to GPS-style sources; they rely on stratum-1 sources over the network. And a stratum-2 server wouldn’t be described as directly linked to a GPS source—the direct link to a GPS clock would define stratum-1, not stratum-2.

In NTP, time is distributed in a hierarchy that starts with a reference clock (such as GPS, WWV, or CDMA) which is considered the stratum-0 source. A server that is directly connected to that reference clock becomes a stratum-1 server. Stratum-2 servers obtain their time from one or more stratum-1 servers over the network, and stratum-3 servers obtain theirs from stratum-2 servers, again over the network, continuing outward with each hop adding one to the stratum level. So a stratum-3 server getting its time via an NTP network path from a stratum-2 server is exactly how the hierarchy is designed to propagate time.

The other statements don’t fit how NTP levels are structured. Stratum-0 devices aren’t servers on the network; they’re the reference clocks that feed stratum-1. A stratum-1 server is connected directly to that reference clock, not via a network path to the clock itself. Stratum-2 servers aren’t directly linked to GPS-style sources; they rely on stratum-1 sources over the network. And a stratum-2 server wouldn’t be described as directly linked to a GPS source—the direct link to a GPS clock would define stratum-1, not stratum-2.