We recommend that the time service for your network be derived from the public NTP servers available on the IP Internet. Two mechanisms are available: an access list-based restriction scheme and an encrypted authenticationĬisco’s implementation of NTP does not support stratum 1 service it is not possible to connect to a radio or atomic clock. The time kept on a device is a critical resource you should use the security features of NTP to avoid the accidental or malicious However, in that case, information flow is one-way only. This alternative reduces configuration complexity because each device can simply be configured to send or However, in a LAN environment, NTP can be configured to use IP broadcast
Accurate timekeeping is possible by exchanging NTP messagesīetween each pair of devices with an association. The IP address of all devices with which it should form associations. The communications between devices running NTP (known as associations) are usually statically configured each device is given Than the others, even if its stratum is lower. NTP also compares the time reported by several devices and does not synchronize to a device whose time is significantly different NTP avoids synchronizing to a device whose time might not be accurate by never synchronizing to a device that is not synchronized. This strategy effectively builds a self-organizing tree of NTP speakers. A device running NTP automatically chooses as its time source the device with the lowest stratum number with which itĬommunicates through NTP. A stratum 1 time server has a radio orĪtomic clock directly attached, a stratum 2 time server receives its time through NTP from a stratum 1 time server, and so NTP uses the concept of a stratum to describe how many NTP hops away a device is from an authoritative time source. Minute is necessary to synchronize two devices to within a millisecond of one another. NTP is extremely efficient no more than one packet per NTP then distributes this time across the network. It is backward compatible with version 3, specified in RFC 1305.Īn NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock attached The current protocol is version 4 (NTPv4), which is a proposed standard as documented in NTP runs over User Datagram Protocol (UDP), which runs over The NTP is designed to time-synchronize a network of devices. Time is available only for display purposes and is not redistributed. 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). You can configure information about the local time zone and summer time (daylight saving time) so that the time appears The system clock keeps track of time internally based on Coordinated Universal Time (UTC), also known as Greenwich Mean Time The system clock can provide time to these services: The system clock can then be set from these sources: This clock runs from the moment the system starts up and keeps track of The basis of the time service is the system clock.
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You can manage the system time and date on your device using automatic configuration methods (RTC and NTP), or manual configuration methods.įor complete syntax and usage information for the commands used in this section, see the Cisco IOS Configuration Fundamentals Command Referenceon. Information About Administering the Device Feature History for Device Administration.Additional References for Device Administration.Example: Configuring Unicast MAC Address Filtering.Example: Adding the Static Address to the MAC Address Table.Example: Configuring MAC Threshold Notification Traps.Example: Configuring MAC Address Change Notification Traps.Configuration Examples for Device Administration.Monitoring and Maintaining Administration of the Device.Configuring Unicast MAC Address Filtering.Adding and Removing Static Address Entries.Configuring MAC Threshold Notification Traps.Configuring MAC Address Move Notification Traps.Configuring MAC Address Change Notification Traps.Configuring a Message-of-the-Day Login Banner.Configuring Summer Time (Daylight Saving Time).
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