Sntp Modes - Cisco SX350 Series Administration Manual

Administration: Time Settings

SNTP Modes

SNTP Modes
Cisco Sx350, SG350X, SG350XG, Sx550X & SG550XG Series Managed Switches, Firmware Release 2.2.5.x
Time Zone and Daylight Savings Time (DST)
The Time Zone and DST can be set on the device in the following ways:
• Dynamic configuration of the device through a DHCP server, where:
- Dynamic DST, when enabled and available, always takes precedence over the
manual configuration of DST.
- If the server supplying the source parameters fails, or dynamic configuration is
disabled by the user, the manual settings are used.
- Dynamic configuration of the time zone and DST continues after the IP address
lease time has expired.
• Manual configuration of the time zone and DST becomes the Operational time zone
and DST, only if the dynamic configuration is disabled or fails.
The DHCP server must supply DHCP option 100 in order for dynamic time zone
NOTE
configuration to take place.
The device can receive system time from an SNTP server in one of the following ways:
• Client Broadcast Reception (passive mode)—SNTP servers broadcast the time, and
the device listens to these broadcasts. When the device is in this mode, there is no need
to define a Unicast SNTP server.
• Client Broadcast Transmission (active mode)—The device, as an SNTP client,
periodically requests SNTP time updates. This mode works in either of the following
ways:
- SNTP Anycast Client Mode—The device broadcasts time request packets to all
SNTP servers in the subnet, and waits for a response.
- Unicast SNTP Server Mode—The device sends Unicast queries to a list of
manually-configured SNTP servers, and waits for a response.
The device supports having all of the above modes active at the same time and selects the best
system time received from an SNTP server, according to an algorithm based on the closest
stratum (distance from the reference clock).
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