268 Managing General System SettingsWhy is the System Time Needed?The switch uses the system clock to provide time stamps on log messages.Additionally, some show commands include the time in the commandoutput. For example, the show users login-history command includes a LoginTime field. The system clock provides the information for the Login Timefield.How Does SNTP Work?SNTP assures accurate switch clock time synchronization. Timesynchronization is performed by a network SNTP server.Time sources are established by Stratums. Stratums define the accuracy ofthe reference clock. The higher the stratum (where zero is the highest), themore accurate the clock. The switch is at a stratum that is one lower than itstime source. For example, if the SNTP server in an internal network is aStratum 3 device, the switch is a Stratum 4 device.You can configure the switch to request the time from an SNTP server on thenetwork, or you can allow the switch to receive SNTP broadcasts.Requesting the time from a unicast SNTP server is more secure. Use thismethod if you know the IP address of the SNTP server on your network. If youallow the switch to receive SNTP broadcasts, any clock synchronizationinformation is accepted, even if it has not been requested by the device. Thismethod is less secure than polling a specified SNTP server.To increase security, you can require authentication between the configuredSNTP server and the SNTP client on the switch. Authentication is providedby Message Digest 5 (MD5). MD5 verifies the integrity of thecommunication and authenticates the origin of the communication.Default General System InformationBy default, no system information or time information is configured, and theSNTP client is disabled. The default SDM Template applied to the switch isthe Dual IPv4-IPv6 template.
