A Cisco firewall keeps an internal clock that can be used for Syslog time stamps, certificate time stamps, and so on. The clock is powered by a battery in the absence of regular power.
The internal clock is always based on Coordinated Universal Time (UTC). UTC was previously known as Greenwich Mean Time (GMT).
You can set the system time using two different approaches:
Manually— You set the time and date on the firewall along with the time zone and specify whether to observe daylight savings time. With manual configuration, the firewall clock is only as accurate as the internal clock hardware.
Using Network Time Protocol (NTP)— This is a protocol defined by RFC 1305 that provides a mechanism for the devices in ...