12.1.2 Client function

<Structure of this section>

(1) Connection type

(a) Unicast client

If the host NTP server is a unicast server, setting the host NTP server in the configuration command ntp server enables the Switch to act as a unicast client and synchronize with the server's time.

(b) Broadcast client

If the host NTP server is a broadcast server, setting the configuration command ntp broadcast client allows the Switch to act as a broadcast client and synchronize with the server time.

(2) Authentication

The following tables show the authentication keys that are assigned to NTP messages sent and received by the Switch as NTP clients.

Table 12-2: Authentication keys used when the Switch operates as a NTP client-
Connection mode of this equipment	Transmission from the Switch	Reception by the Switch
Unicast client	Authentication key specified in key parameter of the configuration command ntp server	Any authentication key (authentication key set in the Switch configuration)
Broadcast client	No transmission

(3) Selecting Host NTP Servers

If you have more than one parent NTP server in your system, select the most appropriate NTP server according to the following steps: (a) Determining if there is a synchronous mismatch to (c) Cluster algorithm. The operating status of the connected NTP servers can be checked using the operation-command show ntp associations.

(a) Determining Synchronization Failure

Exclude NTP servers that meet any of the following criteria from NTP servers to which you select synchronization destinations:

Table 12-3: Synchronization failure conditions
Nonconforming condition	Description
NTP Servers Cannot Synchronize	NTP servers are asynchronous LI flag of the received NTP message3
NTP Servers Cannot Synchronize	Stratum on NTP servers are not compatible Stratum of received NTP messaging ≧ 16
Distance-limit of NTP servers	Route distance of NTP servers*> 1 second + delay time generated at polling interval
Looping status (the synchronization destination of NTP servers is the Switch)	Reference ID(ref id of NTP server is IP addressof the Switch
Status with no communication	Reach of NTP servers = 0 (no reception in the last 8 transmissions)

#: Root Dispersion of messages received from NTP servers with prefer parameter is limited to a maximum of 500 milliseconds.

(b) Intersection algorithm

The "offset ± route distance" of every candidate finds the lower limit (low) and upper limit (high) overlapping with the most candidates. Of these, offset will truechimer candidates within low~high (appropriate candidates) and falseticker out-of-range candidates (inappropriate candidates) to exclude falseticker from the candidates. However, NTP servers with prefer parameter are always truechimer.

The following figure shows an example of selecting an intersection algorithm. In this case, the interval where the most candidates overlap is between 10.5 and 12.2, and Candidate 1 is falseticker and excluded.

Figure 12-2: Example of intersection algorithm selection

(c) Cluster algorithm

By looking at offset's jitter among the candidates, we narrow down to the extent that more offset are gathered, and exclude candidates that are out of the group (outlier).

If the current destination NTP server is among the remaining candidates, select the current destination NTP server as the synchronization destination. Otherwise, select the candidate with the lowest stratum value (or the smaller route distance if stratum values are the same) from the remaining candidates as the destination.

If there is a candidate with prefer parameter specified, filtering is disabled and the candidate is unconditionally synchronized.