Cisco routers, like all computers, keep track of time. While the time of day is unimportant to the router, it is of some importance to us, especially if system logging, accounting, and SNMP are enabled. When you configure your router, you need to set its clock, either manually each time the router reboots, or by using the Network Time Protocol (NTP).
Cisco 7x00 series routers use a hardware clock. On all other models when the system boots up the clock is set to March 1, 1993.
IOS uses Universal Time Coordinated (UTC), more commonly known as Greenwich Mean Time (GMT). This means that if you want your logging and accounting information to reflect local time, you need to set your time zone and its offset ...