Configuring Ntp Servers With Local Sources; Using A Load Balancer; Verifying The Ntp Configuration - Cisco ASR 5500 Administration Manual

System Settings
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
• Enter the IP address of NTP servers using IPv4 dotted-decimal or IPv6 colon-separated-hexadecimal
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
balancer may distribute those packets dynamically and confuse the NTP client. NTP packets are latency and
jitter sensitive. Relaying them through a load balancer can confuse the NTP client and is not a supported
practice.

Verifying the NTP Configuration

Verify the NTP configuration is correct. Enter the following command at the Exec mode prompt:
show ntp associations
The output displays information about all NTP servers. See the output below for an example deploying two
NTP servers.
+----Peer Selection: ( ) - Rejected / No Response
|
|
|
|
|
server ip_address3
end
chapter in the Command Line Interface Reference for more information.
notation.
Configure the system with at least three (preferably four) NTP servers.
(x) - False Tick
(.) - Excess
(-) - Outlyer
(+) - Candidate
(#) - Selected
Configuring NTP Servers with Local Sources
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