Network Router User Manual

3-7
Cisco ONS 15530 Configuration Guide and Command Reference
78-14227-01, Cisco IOS Release 12.1(10)EV2
Chapter 3 Initial Configuration
Configuring NTP
NTP has two ways to avoid synchronizing to a machine whose time might be ambiguous:
• NTP never synchronizes to a machine that is not synchronized itself.
• NTP compares the time reported by several machines and does not synchronize to a machine whose
time is significantly different from the others, even if its stratum is lower.
The communications between machines running NTP, known as associations, are usually statically
configured; each machine is given the IP address of all machines with which it should form associations.
Accurate timekeeping is possible by exchanging NTP messages between each pair of machines with an
association.
The Cisco implementation of NTP does not support stratum 1 service; it is not possible to connect to a
radio or atomic clock. We recommend that you obtain the time service for your network from the public
NTP servers available in the IP Internet. If the network is isolated from the Internet, the Cisco NTP
implementation allows a machine to be configured so that it acts as though it is synchronized using NTP,
when in fact it has determined the time using other means. Other machines then synchronize to that
machine using NTP.
A number of manufacturers include NTP software for their host systems, and a version for systems
running UNIX and its various derivatives is also publicly available. This software allows host systems
to be time-synchronized as well.
Configuring NTP
NTP services are enabled on all interfaces by default. You can configure your Cisco ONS 15530 in either
of the following NTP associations:
• Peer association—This system either synchronizes to the other system or allows the other system to
synchronize to it.
• Server association—This system synchronizes to the other system, and not the other way around.
From global configuration mode, use the following procedure to configure NTP in a server association
that transmits broadcast packets and periodically updates the calendar:
For information on other optional NTP configurations, see the Cisco IOS Configuration Fundamentals
Configuration Guide.
Command Purpose
Step 1
Switch(config)# ntp update-calendar Updates hardware calendar with NTP time.
Step 2
Switch(config)# ntp server ip-address Forms a server association with another system. You can
specify multiple associations.
Step 3
Switch(config)# end
Switch#
Returns to privileged EXEC mode.
Step 4
Switch# copy system:running-config
nvram:startup-config
Saves your configuration changes to NVRAM.