This alternative reduces configuration complexity because each device can simply be configured to send or receive broadcast messages. However, in a LAN environment, NTP can be configured to use IP broadcast messages instead. Accurate timekeeping is possible by exchanging NTP messages between each pair of devices with an association. The communications between devices running NTP (known as associations) are usually statically configured each device is given the IP address of all devices with which it should form associations. NTP also compares the time reported by several devices and does not synchronize to a device whose time is significantly different than the others, even if its stratum is lower. 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 it communicates through NTP.
A stratum 1 time server has a radio or atomic clock directly attached, a stratum 2 time server receives its time through NTP from a stratum 1 time server, and so on. NTP uses the concept of a stratum to describe how many NTP hops away a device is from an authoritative time source. NTP is extremely efficient no more than one packet per minute is necessary to synchronize two devices to within a millisecond of one another. NTP then distributes this time across the network. NTP is documented 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 to a time server. NTP runs over User Datagram Protocol (UDP), which runs over IP. The NTP is designed to time-synchronize a network of devices. For configuration information, see the “Configuring Time and Date Manually” section. If it is not authoritative, the 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 correctly for the local time zone. The system clock keeps track of time internally based on Universal Time Coordinated (UTC), also known as Greenwich Mean Time (GMT). 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 date and time. The heart of the time service is the system clock. These sections contain this configuration information: Note For complete syntax and usage information for the commands used in this section, see the Cisco IOS Configuration Fundamentals Command Reference, Release 12.4.
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. Unless otherwise noted, the term switch refers to a Catalyst 3750-X or 3560-X standalone switch and to a Catalyst 3750-X switch stack.
This chapter describes how to perform one-time operations to administer the Catalyst 3750-X or 3560-X switch.
Configuring LLDP, LLDP-MED, and Wired Location Service.Configuring DHCP Features and IP Source Guard.Configuring Resilient Ethernet Protocol.Configuring Optional Spanning-Tree Features.
Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling.Configuring IEEE 802.1x Port-Based Authentication.Configuring Switch-Based Authentication.Assigning the Switch IP Address and Default Gateway.Configuring Cisco IOS Configuration Engine.Catalyst 3750-X and 3560-X Switch Software Configuration Guide, Cisco IOS 15.0(2)SE and Later.