Cisco ASR 5500 System Administration Guide

Do not configure any external NTP servers using the prefer keyword. The NTP clock selection algorithms
already have the built-in ability to pick the best server. Use of prefer usually results in a poorer choice
than NTP can determine for itself.
Important
Do not change the maxpoll, minpoll, or version keyword settings unless instructed to do so by Cisco
TAC.
Important
Use the following example to configure the necessary NTP association parameters:
configure
ntp
enable
server ip_address1
server ip_address2
server ip_address3
end
Notes:
•
By default context_name is set to local. This is the recommended configuration.
•
A number of options exist for the server command. Refer to the NTP Configuration Mode Commands
chapter in the Command Line Interface Reference for more information.
•
Enter the IP address of NTP servers using IPv4 dotted-decimal or IPv6 colon-separated-hexadecimal
notation.
Configure the system with at least three (preferably four) NTP servers.Important
Save the configuration as described in the Verifying and Saving Your Configuration chapter.
Configuring NTP Servers with Local Sources
NTP can use network peers, local external clocks (such as GPS devices), or a local clock with no external
source.
A local clock with no external source is usually a last-resort clock when no better clock is available. It is
typically configured on a site's intermediate NTP server so that when a WAN network outage occurs, hosts
within the site can continue to synchronize amongst themselves.
You can configure this in ntpd or on many commercially available NTP devices. This local clock should
always have a high stratum number (8+) so that under normal conditions (when real sources are available)
this local clock will not be used.
Using a Load Balancer
The NTP daemon and protocol assume that each configured server is running NTP. If a NTP client is configured
to synchronize to a load balancer that relays and distributes packets to a set of real NTP servers, the load
ASR 5500 System Administration Guide, StarOS Release 21.5
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System Settings
Configuring NTP Servers with Local Sources

Cisco ASR 5500 Specifications

General

Brand	Cisco
Model	ASR 5500
Category	Network Router
Language	English