Cisco IE 4000, Software Configuration Manual

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Cisco Systems, Inc. www.cisco.com
Performing Switch Administration
This chapter describes how to perform one-time operations to administer your switch.
Information About Performing Switch Administration
System Time and Date Management
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.
System Clock
The basis of 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:

NTP

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 appears correctly 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
Configuring Time and Date Manually, page 111 .
Network Time Protocol
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.
NTP uses the concept of a stratum to describe how many NTP hops away a device is from an authoritative time source.
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. A device running NTP automatically chooses as its time source the device
with the lowest stratum number with which it communicates through NTP. This strategy effectively builds a
self-organizing tree of NTP speakers.