Cisco WS-C3560-48PS-S Software Configuration Manual page 125

Chapter 6 Administering the Switch
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 6-1
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.
Figure 6-1
Local
workgroup
servers
Workstations
If the network is isolated from the Internet, Cisco's implementation of NTP allows a device to act as
though it is synchronized through NTP, when in fact it has determined 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.
78-16156-01
shows a typical network example using NTP. Switch A is the NTP master, with Switches B,
Typical NTP Network Configuration
Switch B
Switch E
Switch F
Workstations
Managing the System Time and Date
Switch A
Switch C
Catalyst 3560 Switch Software Configuration Guide
Switch D
6-3