NTP (Network Timing Protocol)

NTP (Network Timing Protocol)

NTP allows time synchronization in to the source clock. NTP uses UDP port 123 to communicate. There are 3 modes of operation.

- Client

- Server

- Symmetric active mode (peer)

We can statically configure server address or let it discover by itself using broadcast command. In this example below, I will show the configuration of statically address configuration.

For broadcast, click here.

Example 

  - Network 192.168.1.1 between R1 and R2

  - Authentication ntp

R1
ntp authentication-key 1 md5 121711075F00091D 7
ntp authenticate
ntp master
!

R2

ntp authentication-key 1 md5 1419061B410F2F32 7

ntp authenticate

ntp trusted-key 1

//Client

ntp server 192.168.1.1 key 1   

//Peer 

ntp peer 192.168.1.1 key 1

Verify configuration 

debug ntp packet

debug ntp authentication

debug ntp event

Mar  1 00:44:37.109:  Authentication key 1

Mar  1 00:44:37.113: NTP: 192.168.1.1 synced to new peer

Mar  1 00:44:37.113: NTP: sync change

Mar  1 00:44:37.113: NTP: peer stratum change

Mar  1 00:44:37.113: NTP: 192.168.1.1 reachable

Check the synchronization between routers

R2#show ntp associations

      address         ref clock     st  when  poll reach  delay  offset    disp

*~192.168.1.1      127.127.7.1       8    30    64   17    59.7  -51.09  1939.3

 * master (synced), # master (unsynced), + selected, - candidate, ~ configured

R2#

R2#sh ntp status

Clock is synchronized, stratum 9, reference is 192.168.1.1

nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**18

reference time is C0294E35.201800AA (00:47:49.125 UTC Fri Mar 1 2002)

clock offset is -51.0852 msec, root delay is 59.68 msec

root dispersion is 1990.42 msec, peer dispersion is 1939.30 msec

R2#