Dell PowerConnect 5524P User Manual page 173

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.
• If there is a tie in stratums, packets from servers defined on the device are
preferred to Anycast packets, which in turn are preferred to Broadcast
packets.
• If multiple servers pass the above criteria, then the server that sent the first
(earliest) time packet is chosen.
If a better server is discovered later, it is selected to be the "designated server"
at that time.
Polling
You can configure the system to acquire time information in the following
ways:
• Enable polling — Time information is requested every polling interval.
• Do not enable polling — Time information is received when the system is
brought up and every time that a topological change is made to the
Running Configuration file, for example when an SNTP Unicast server is
added.
This is configured by the user in the SNTP Global Settings page.
On power up, when the switch sends a request and there is no reply, it issues
another request (three retries at most) after 20 seconds of waiting.
If no SNTP server is found, the process is invoked every "poll interval" (set in
the SNTP Global Settings page), and a management trap is triggered.
Authentication
You can require that SNTP servers be authenticated, although this is not
mandatory (see the SNTP Authentication pages).
Dell PowerConnect 55xx Systems User Guide
173