Association Modes - H3C SR6600-X Configuration Manual

Figure 27 NTP architecture
Tertiary servers
(Stratum 3)
Quaternary servers
(Stratum 4)
Server
Typically, 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. The accuracy of each server is the stratum,
with the topmost level (primary servers) assigned as one and each level downwards in the hierarchy
assigned as one greater than the preceding level. NTP uses a stratum to describe how many NTP hops
away a device is from the primary time 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
Authoritative
clock
Primary servers
(Stratum 1)
Secondary servers
(Stratum 2)
Symmetric
Client
peer
Symmetric Broadcast/multicast
peer server
67
Broadcast/multicast
client