Basic NTP Configuration

I will call this NTP Scenario 1: Basic NTP with no authentication. There will be more blogs about NTP but this is just to get it started.

R4, R5, and R6 are connected via full mesh frame-relay
R6 will be the NTP server.

First set the clock on R6:

R6#clock set 15:47:30 31 May 2008
*May 31 15:47:30.003: %SYS-6-CLOCKUPDATE: System clock has been updated from 01:
05:19 UTC Fri Mar 1 2002 to 15:47:30 UTC Sat May 31 2008, configured from consol
e by console.

Verify the time with show clock:

R6#show clock
15:47:36.651 UTC Sat May 31 2008

Configure R6 as the master along with stratum:

R6#conf t
R6(config)#ntp master ?
<1-15> Stratum number


R6(config)#ntp master 3
R6(config)#^Z

Verify that R6 is synced with itself:

R6#show ntp associations

address ref clock st when poll reach delay offset disp
*~127.127.7.1 127.127.7.1 2 22 64 1 0.0 0.00 15875.
* master (synced), # master (unsynced), + selected, - candidate, ~ configured

R6#show ntp status
Clock is synchronized, stratum 3, reference is 127.127.7.1
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24
reference time is CBEBF22C.1583DCD8 (15:50:04.084 UTC Sat May 31 2008)
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 15875.02 msec, peer dispersion is 15875.02 msec

Now it's time to configure the clients, let's first check the time on R4:

R4#show clock
*03:03:44.823 UTC Fri Mar 1 2002
R4#conf t
R4(config)#ntp server 172.12.45.6
R4(config)#^Z
R4#show clock
*03:04:52.047 UTC Fri Mar 1 2002
R4#

Notice the time is 6 years behind the current date, I have noticed that NTP will not sync when the times are so far apart (Not sure how this works, but let's manually 'push' R4 a little closer)

R4#clock set 15:30:40 31 May 2008

Now we're about 15 minutes behind. Let's do some debugging:

R4#debug ntp sync
NTP clock synchronization debugging is on

.May 31 15:31:43.107: NTP: synced to new peer 172.12.45.6

Noe that we're synced let's verify on R6 and R4:

R4#show clock
15:59:42.466 UTC Sat May 31 2008

R6#show clock
15:59:41.135 UTC Sat May 31 2008

Looks good. I will use this topology for other NTP labs so stay tuned...