Cisco 2950G 24 Software Configuration Guide - Page 186
Managing the System Time and Date, Understanding the System Clock, Understanding Network Time Protocol
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Managing the System Time and Date Chapter 7 Administering the Switch Managing the System Time and Date You can manage the system time and date on your switch using automatic configuration, such as the Network Time Protocol (NTP), or manual configuration methods. Note For complete syntax and usage information for the commands used in this section, refer to the Cisco IOS Configuration Fundamentals Command Reference for Release 12.1. This section contains this configuration information: • Understanding the System Clock, page 7-34 • Understanding Network Time Protocol, page 7-34 • Configuring NTP, page 7-36 • Configuring Time and Date Manually, page 7-43 Understanding the System Clock The heart of the time service is the system clock. This clock runs from the moment the system starts up and keeps track of the date and time. The system clock can then be set from these sources: • Network Time Protocol • Manual configuration The system clock can provide time to these services: • User show commands • Logging and debugging messages The system clock keeps track of time internally based on Universal Time Coordinated (UTC), also known as Greenwich Mean Time (GMT). You can configure information about the local time zone and summer time (daylight saving time) so that the time is correctly displayed for the local time zone. The system clock keeps track of whether the time is authoritative or not (that is, whether it has been set by a time source considered to be authoritative). If it is not authoritative, the time is available only for display purposes and is not redistributed. For configuration information, see the "Configuring Time and Date Manually" section on page 7-43. Understanding Network Time Protocol The NTP is designed to time-synchronize a network of devices. NTP runs over User Datagram Protocol (UDP), which runs over IP. NTP is documented in RFC 1305. An NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two devices to within a millisecond of one another. 7-34 Catalyst 2950 Desktop Switch Software Configuration Guide 78-14982-01
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