78
Figure 33
NTP architecture
A stratum 1 NTP server gets its time from an authoritative time source, such as an atomic clock. It
provides time for other devices as the primary NTP server. A stratum 2 time server receives its time
from a stratum 1 time server, and so on.
To ensure time accuracy and availability, you can specify multiple NTP servers for a device. The
device selects an optimal NTP server as the clock source based on parameters such as stratum. The
clock that the device selects is called the reference source. For more information about clock
selection, see the related protocols and standards.
If the devices in a network cannot synchronize to an authoritative time source, you can perform the
following tasks:
•
Select a device that has a relatively accurate clock from the network.
•
Use the local clock of the device as the reference clock to synchronize other devices in the
network.
Association modes
NTP supports the following association modes:
•
Client/server mode
•
Symmetric active/passive mode
•
Broadcast mode
•
Multicast mode
Secondary servers
(Stratum 2)
Primary servers
(Stratum 1)
Authoritative
clock
Tertiary servers
(Stratum 3)
Quaternary servers
(Stratum 4)
Server
Client
Symmetric
peer
Symmetric
peer
Broadcast/multicast
server
Broadcast/multicast
client
