Switch Management
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Guide\Dell_Astute_SwitchManagement.fm
D E L L CO N F I D E N T I A L – P R E L I M I N A RY 8 / 9 / 16 - F O R P RO O F O N L Y
•
Broadcast
Broadcast information is used if receiving Broadcast packets has been
enabled, and one of the following situations occurs:
–
The SNTP server IP address has not been defined.
–
Several time-information packets are received and the Broadcast time
is best according to the algorithm defined in
Broadcast is the least secure method of receiving time, because it is both
unsecured and the time information was not specifically requested by the
device. Anycast is also unsecured, but time-information packets are only
accepted if they were requested.
Stratums
Each SNTP server is characterized by stratums, which define the accuracy of
its clock. The stratum is the distance, in terms of NTP hops, from the most
authoritative time server. The lower the stratum (where zero is the lowest),
the more accurate the clock. The switch accepts time from stratum 1 and
above.
The following provides examples of clocks from various stratums:
•
Stratum 0
— A real time clock is used as the time source, for example, a
GPS system.
•
Stratum 1
— A server that is directly linked to a Stratum 0 time source is
used.
•
Stratum 2
— The time source is distanced from the Stratum 1 server over
a network path, for example, a Stratum 2 server receives the time over a
network link, via NTP, from a Stratum 1 server.
Algorithm for Selecting Designated SNTP Server
Messages received from SNTP servers are logged, until there are three
responding servers, or the timer expires. In any event, when the third message
is received, the timer expires.
A server is selected to be the “designated server” according to the following
criteria:
• The stratum (the distance in terms of NTP hops from the best
authoritative time servers) is considered, and the server with the best
(lowest) stratum is selected.
