Configure NTP on Cisco router
Network Time Protocol (NTP) is an application layer protocol used to synchronizate clocks between computers on a TCP/IP network. The goal of NTP is to ensure that all devices on a network agree on the time, since even a small difference can create problems.
Cisco routers can be configure as NTP clients with the following command:
R1(config)#ntp server 10.0.0.200
The command above specified that the server with the IP address of 10.0.0.200 will be used for time synchronization by our device. We can check whether the time synchronization was successful by using the show ntp status command:
R1#show ntp status Clock is synchronized, stratum 2, reference is 10.0.0.200 nominal freq is 250.0000 Hz, actual freq is 249.9990 Hz, precision is 2**19 reference time is D947B82E.00000181 (14:54:38.385 UTC Fri Aug 7 2015) clock offset is 0.00 msec, root delay is 0.00 msec root dispersion is 0.02 msec, peer dispersion is 0.02 msec.
NTP uses the well-known UDP port 123, so make sure that the connectivity exists between the NTP client and NTP server.