Dell PowerConnect 5548 User Guide - 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