Chapter 7 Administering the Switch

Managing the System Time and Date

Figure 7-1shows a typical network example using NTP. Switch A is the NTP master, with Switches 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.

Figure 7-1 Typical NTP Network Configuration

Switch A

Local

workgroup

servers

Switch B

 

Switch C

Switch D

 

 

 

 

Switch E

Workstations

Switch F

Workstations

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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.

Configuring NTP

The switch does not have a hardware-supported clock and cannot function as an NTP master clock to which peers synchronize themselves when an external NTP source is not available. The switch also has no hardware support for a calendar. As a result, the ntp update-calendarand the ntp master global configuration commands are not available.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

 

OL-9775-02

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Cisco Systems 3750E manual Configuring NTP, Typical NTP Network Configuration