Cisco Catalyst 3750-E Series, Software Configuration Manual

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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
Chapter 7 Administering the Switch
Managing the System Time and Date
Cisco’s implementation of NTP does not support stratum 1 service; it is not possible to connect to a radio
or atomic clock. We recommend that the time service for your network be derived from the public NTP
servers available on the IP Internet.
Figure 7-1 shows a typical network example using NTP. Switch A is the NTP master, with the Switch B,
C, and D configured in NTP server mode, in server association with Switch A. Switch E is configured
as an NTP peer to the upstream and downstream switches, Switch B and Switch F, respectively.
Figure 7-1 Typical NTP Network Configuration
If the network is isolated from the Internet, Cisco’s implementation of NTP allows a device to act as if
it is synchronized through NTP, when in fact it has learned the time by using other means. Other devices
then synchronize to that device through NTP.
When multiple sources of time are available, NTP is always considered to be more authoritative. NTP
time overrides the time set by any other method.
Several manufacturers include NTP software for their host systems, and a publicly available version for
systems running UNIX and its various derivatives is also available. This software allows host systems to
be time-synchronized as well.
Switch F
Switch A
Workstations
Workstations
Local
workgroup
servers
101349
Switch B
Switch E
Switch C Switch D