Courseiva
SystemPrivileged EXEC

show ntp associations

Displays the status of NTP associations configured on the device, used to verify NTP synchronization and identify time sources.

Syntax·Privileged EXEC
show ntp associations

When to Use This Command

  • Verify that the router is synchronized to an NTP server after configuration.
  • Troubleshoot time synchronization issues when logs show incorrect timestamps.
  • Check the stratum level of NTP peers to ensure accurate time source hierarchy.
  • Monitor NTP associations during network maintenance to confirm redundancy.

Command Examples

Basic NTP associations display

show ntp associations
  address         ref clock     st  when  poll reach  delay  offset   disp
*~192.168.1.10    .GPS.            1   23    64   377   0.512  0.123   0.015
+~10.0.0.1        .LOCL.           8   12   128   377   1.023  0.456   0.032
 ~192.168.2.20    .NIST.           2    -    64     0   0.000  0.000 16000.0
 * sys.peer, # selected, + candidate, - outlyer, ~ configured

Line 1: Header. Line 2: * indicates sys.peer (synchronized), ~ configured, address 192.168.1.10, ref clock .GPS. (stratum 1 GPS), st=1, when=23 sec ago, poll=64 sec, reach=377 (good), delay=0.512ms, offset=0.123ms, disp=0.015ms. Line 3: + candidate peer, ~ configured, 10.0.0.1 with stratum 8 local clock, reach=377, offset 0.456ms. Line 4: ~ configured but unreachable (reach=0), disp=16000 (high dispersion). Legend explains symbols.

NTP associations with detail

show ntp associations detail
192.168.1.10 configured, our_master, sane, valid, stratum 1
ref ID .GPS., time D6A1B2C3.45678901 (13:45:23.123 UTC Mon Jan 15 2024)
our mode client, peer mode server, our poll intvl 64, peer poll intvl 64
root delay 0.00 msec, root disp 0.02 msec, reach 377, sync dist 0.015
 delay 0.512 msec, offset 0.123 msec, dispersion 0.015 msec
 precision 2**16, version 4
org time D6A1B2C3.45678901
rec time D6A1B2C3.45678901
 xmt time D6A1B2C3.45678901
filtdelay =     0.51    0.52    0.53    0.51    0.50    0.52    0.51    0.53
filtoffset =    0.12    0.13    0.12    0.11    0.12    0.13    0.12    0.11
filterror =     0.02    0.03    0.02    0.02    0.03    0.02    0.03    0.02

Shows detailed per-association info: configured, our_master (synchronized), stratum 1, ref ID .GPS., timestamps, poll intervals, reach 377 (good), delay and offset values, and filter data showing recent samples. Good values: low delay/offset, reach 377, stratum low. Bad: reach 0, high dispersion.

Understanding the Output

The 'show ntp associations' output displays each configured NTP peer or server. The first character indicates status: '*' means the peer is the system peer (synchronized to), '#' is selected but not sys.peer, '+' is a candidate, '-' is outlyer, '~' is configured. 'address' is the NTP server IP. 'ref clock' shows the reference clock source (e.g., .GPS., .LOCL.). 'st' is stratum level (1 is most accurate, 16 is unsynchronized). 'when' is seconds since last packet received. 'poll' is poll interval in seconds. 'reach' is an octal reachability register (377 = 8 successful polls). 'delay' is round-trip delay in ms, 'offset' is time difference in ms, 'disp' is dispersion in ms. For a healthy association, look for '*' or '+', reach near 377, low delay and offset (<10ms typical), and low dispersion. High dispersion (>1000) or reach 0 indicates problems. The detail view adds timestamps, filter data, and synchronization state.

CCNA Exam Tips

1.

CCNA exam may ask which symbol indicates the router is synchronized to an NTP server: answer is '*' (sys.peer).

2.

Know that reach value 377 (octal) means all last 8 polls were successful; any lower value indicates packet loss.

3.

Stratum 1 is the most accurate (directly from atomic clock); stratum 16 means unsynchronized.

4.

The 'show ntp status' command is often tested alongside to verify synchronization state.

Common Mistakes

Confusing the '*' symbol with '+' or '#'; only '*' means the router is synchronized to that peer.

Assuming a reach value of 1 means good; actually 377 is perfect, lower values indicate issues.

Forgetting that NTP uses UDP port 123; ACLs or firewalls blocking it cause reach=0.

Related Commands

clock set [hh:mm:ss] [day] [month] [year]

Sets the system clock on a Cisco IOS device from the privileged EXEC mode, used to manually configure the router's time when NTP is not available.

show ntp status

Displays the current NTP synchronization status, including clock stratum, reference clock, and synchronization state, used to verify NTP operation and clock accuracy.

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