CCIE Practical Studies, Volume I

The "Big show" and "Big D" for NTP and SNTP

You have already seen and used the three primary show commands for NTP and SNTP. Those commands are as follows :

• show ntp status ” This command provides detailed status of NTP synchronization, along with the three primary elements of NTP: delay, offset, and dispersion.

• show sntp ” This command displays whether SNTP is configured if it has not found a valid clock source. If SNTP is synchronized, this command displays the IP address and the stratum of the server.

• show ntp associations [detailed] ” This command displays any statically configured NTP peers, along with the clock selection and whether the peer is synchronized.

Example 17-15 lists the output from the show ntp status command. The output details that you want to look for here are that the clock in synchronized, with a valid stratum, usually less then 16. You also need information about a reference clock. The clock offset, root delay, root, and peer dispersion should be relatively small numbers , in the millisecond range, when the clocks are synchronized.

Example 17-15 show ntp status Command Output

ntp_t_client# show ntp status Clock is synchronized, stratum 7, reference is 10.150.10.3 nominal freq is 250.0000 Hz, actual freq is 249.9984 Hz, precision is 2**19 reference time is BD1604F7.3618FF07 (20:41:27.211 UTC Tue Jul 11 2000) Correct time! clock offset is 0.3951 msec, root delay is 3.78 msec root dispersion is 0.44 msec, peer dispersion is 0.03 msec ntp_t_client#

Example 17-16 lists the output from a show ntp status command, where the clock hasn't synchronized. Notice that the stratum is not set and no reference clock exists.

Example 17-16 Bad Output from the show ntp status Command

timex# show ntp stat Clock is unsynchronized, stratum 16, no reference clock nominal freq is 250.0000 Hz, actual freq is 250.0003 Hz, precision is 2**19 reference time is BD15D99C.4AC66EE0 (17:36:28.292 UTC Tue Jul 11 2000) clock offset is -0.1224 msec, root delay is 31.14 msec root dispersion is 1.45 msec, peer dispersion is 0.14 msec timex#

Example 17-17 lists the output from the show sntp command. The relevant information to look for here is the IP address of the SNTP server, a valid stratum, and confirmation that the clock is synchronized. If no valid SNTP broadcasts are found, this command displays only that the SNTP client mode is enabled.

Example 17-17 show sntp Command Output

skynet_2# show sntp SNTP server Stratum Version Last Receive 206.191.241.44 14 3 00:00:44 Synced Bcast Broadcast client mode is enabled.

Example 17-18 lists the output from the show ntp associations command. The key indicator is the *, which indicates that the master clock is synchronized and gives the IP address and stratum of that clock. The bottom of the example lists the extended version of this command, which includes information on delay, offset, and dispersion. The first line of the output provides a quick view of the primary NTP association.

Example 17-18 show ntp associations Command Output

timex# show ntp associations address ref clock st when poll reach delay offset disp *~10.150.10.1 10.150.10.3 7 38 64 377 6.1 -0.51 0.1 * master (synced), # master (unsynced), + selected, - candidate, ~ configured timex# timex# show ntp associations detail 10.150.10.1 configured, our_master, sane, valid, stratum 7 ref ID 10.150.10.3, time BD160B37.3911241E (21:08:07.222 UTC Tue Jul 11 2000) our mode active, peer mode passive, our poll intvl 64, peer poll intvl 64 root delay 3.78 msec, root disp 0.41, reach 377, sync dist 5.432 delay 6.07 msec, offset -0.5087 msec, dispersion 0.09 precision 2**19, version 3 org time BD160B48.A2712FA3 (21:08:24.634 UTC Tue Jul 11 2000) rcv time BD160B48.A3598FCA (21:08:24.638 UTC Tue Jul 11 2000) xmt time BD160B48.A19B718B (21:08:24.631 UTC Tue Jul 11 2000) filtdelay = 6.07 6.04 6.03 6.13 6.03 6.09 6.01 6.06 filtoffset = -0.51 -0.41 -0.40 -0.43 -0.48 -0.43 -0.41 -0.39 filterror = 0.02 0.99 1.97 2.94 3.92 4.90 5.87 6.85 timex#

Cisco provides many debugs for NTP, but perhaps the most useful one is debug ntp select. This debug shows the status of NTP peers, along with the packet exchange as it is occurring. Most of the other debugs indicate only when an event is triggered, such as debug ntp events and debug ntp sync. These display only information when state changes happen and give no indications of internal workings.

Example 17-19 lists the output of the debug ntp select command, which indicates that the output packet is going to the NTP server 10.150.10.3, your configured clock. You also see the offset measured from the survivor clock, which indicates that the clocks have been compared.

Example 17-19 debug ntp select Command Output

03:42:37: NTP: nlist 1, allow 0, found 0, low -0.001984, high 0.002411 03:42:37: NTP: candidate 10.150.10.3 cdist 96.002197 error 0.000305 03:42:37: NTP: survivor 10.150.10.3 offset 0.000226, cdist 96.00220 03:43:23: NTP: nlist 1, allow 0, found 0, low -0.001785, high 0.002151 03:43:23: NTP: candidate 10.150.10.3 cdist 96.001968 error 0.000076 03:43:23: NTP: survivor 10.150.10.3 offset 0.000185, cdist 96.00197 03:43:41: NTP: nlist 1, allow 0, found 0, low -0.002045, high 0.002411 03:43:41: NTP: candidate 10.150.10.3 cdist 96.002228 error 0.000336 03:43:41: NTP: survivor 10.150.10.3 offset 0.000185, cdist 96.00223