A software clock is the operating-system-maintained clock in a network device. Accurate timestamps support security mechanisms and help correlate logs during troubleshooting. View it with show clock; add detail to display the time source and whether the time is authoritative. section 2.1.2 section 2.4
Configure and synchronize the device time with these Cisco IOS operations:
- Set the software clock from privileged EXEC mode with clock set hh:mm:ss month day year. section 2.1.2
- View or set the separate battery-powered hardware calendar with show calendar or calendar set. section 2.1.2
- Synchronize once with clock update-calendar or clock read-calendar; these commands do not maintain continuous synchronization. section 2.1.2
- Configure the time zone with clock timezone in global configuration mode; UTC is the default, and recurring daylight saving time can also be configured. section 2.1.2 section 2.4
Manual setting is not practical for ongoing accuracy. Network Time Protocol synchronizes the software clock over UDP port 123. Configure multiple NTP servers for redundancy; the preferred server can become sys.peer while another remains a candidate. Verify synchronization with show ntp associations, show ntp status, and show clock detail. NTP updates the software clock by default, not the calendar, unless ntp update-calendar is configured. section 2.3.1 section 2.4
R1# show clock detail *08:56:18.831 UTC Mon Aug 28 2023 #1 Time source is hardware calendar #2 #1 The asterisk (*) indicates that the time is not authoritative. #2 R1 learned the date and time from its hardware calendar.
Use the annotated output to identify an unauthoritative clock and confirm that the device learned time from its hardware calendar. section 2.1.2
R1(config)# ntp server 216.239.35.0 prefer #1 R1(config)# ntp server 20.43.94.199 #1 R1(config)# do show ntp associations address ref clock st when poll reach delay offset disp *~216.239.35.0 .GOOG. 1 24 64 377 4 0.726 22.840 6.929 #2 +~20.43.94.199 25.66.230.3 3 25 64 377 9.032 24.786 6.720 #3 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured R1(config)# do show clock detail 13:44:32.959 JST Tue Aug 29 2023 Time source is NTP #4 #1 Configures R1 as an NTP client of two servers, marking one as preferred (optional) #2 Google’s server is marked as sys.peer. #3 Microsoft’s server is marked as candidate. #4 R1’s time source is now NTP.
Use the annotated configuration and verification output to compare preferred and candidate NTP servers and confirm the software clock's NTP source. section 2.3.1
