Specifications

7-3
Cisco AS5x00 Case Study for Basic IP Modem Services
11/24/1999
Section 7 Enabling Management Protocols: NTP, SNMP, and Syslog
Enabling the Network Time Protocol
For more information about system management, refer to Release 12.0
Configuration Fundamentals
Configuration Guide
and
Command Reference
at the following URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/index.htm
Task 1. Enabling the Network Time Protocol
The Network Time Protocol (NTP) provides a common time base for networked routers, servers, and
other devices. A synchronized time enables you to correlate syslog and Cisco IOS debug output to
specific events. For example, you can find call records for specific users within one millisecond.
Comparing logs from various networks is essential for:

Troubleshooting

Fault analysis

Security incident tracking
Without precise time synchronization between all the various logging, management, and AAA
functions, time comparisons are not possible.
An NTP enabled network usually gets its time from an authoritative time source, such as a Cisco router,
radio clock, or an atomic clock attached to a timeserver. NTP then distributes this time across the
network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize
two machines to within a millisecond of one another. NTP runs over UDP, which in turn runs over IP.
Note
For more information, refer to the following URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/fun_c/
fcprt3/fcgenral.htm
Step 1
Locate an authoritative clock source. For example, you can use a Cisco router or an atomic clock that
is attached to a time server.
Step 2
Specify the primary NTP server IP address and automatic calendar updates as shown below:
!
ntp update-calendar
ntp server 172.22.66.18 prefer
!
Step 3
Verify that the clock is synchronized to the NTP server. Inspect the status and time association.
Clock sources are identified by their stratum levels. The following example shows a stratum level five
clock.
5300-NAS#show ntp status
Clock is synchronized, stratum 5, reference is 172.22.66.18
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24
reference time is BB944312.4451C9E7 (23:11:30.266 PDT Wed Sep 22 1999)
clock offset is 0.5343 msec, root delay is 13.26 msec
root dispersion is 18.02 msec, peer dispersion is 0.09 msec
5300-NAS#