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.
Definition: show ntp status is a Cisco IOS privileged exec command. Displays the current NTP synchronization status, including clock stratum, reference clock, and synchronization state, used to verify NTP operation and clock accuracy.
Overview
The 'show ntp status' command is a vital diagnostic tool in Cisco IOS that displays the current Network Time Protocol (NTP) synchronization state of the device. NTP is a networking protocol used to synchronize clocks between computer systems over packet-switched, variable-latency data networks. In a network environment, accurate timekeeping is critical for logging events, correlating logs from multiple devices, ensuring proper operation of time-sensitive protocols (such as 802.1X, Kerberos, and routing protocols like OSPF that use timestamps), and meeting compliance requirements.
This command provides a snapshot of the device's NTP status, including the clock stratum (a measure of the clock's distance from the reference clock), the reference clock source (the NTP server or peer the device is synchronized to), the synchronization state (e.g., synchronized, unsynchronized), and other parameters like the clock offset, frequency drift, and last update time. Network engineers reach for this command when verifying NTP configuration after initial setup, troubleshooting time synchronization issues (e.g., logs showing incorrect timestamps, authentication failures due to time skew), or monitoring NTP health as part of routine network maintenance. Unlike 'show ntp associations', which lists all configured NTP peers and servers and their reachability, 'show ntp status' focuses on the device's own clock state and the quality of synchronization.
It is often used in conjunction with 'show ntp associations detail' to get a complete picture. The command runs in privileged EXEC mode (enable mode) and does not require any additional privileges. It has no impact on the running configuration; it is a read-only show command.
Output is typically displayed immediately, though in some cases with many associations or high CPU load, there may be a slight delay. Understanding the output is essential for CCNA and CCNP candidates, as NTP is a foundational service in enterprise networks. The command reveals whether the device is synchronized to a reliable time source, which stratum it believes it is at, and whether the clock is stable.
For example, a stratum 1 device is directly connected to a highly accurate reference clock (like GPS or atomic clock), while a stratum 2 device synchronizes to a stratum 1 server, and so on. The command also shows the 'reference clock ID' (the IP address of the NTP server or peer) and the 'last update' time, which indicates how recently the clock was adjusted. A healthy output shows 'Clock is synchronized, stratum 2, reference is 192.168.1.1' with a low offset (e.g., under 100 ms).
Problem indicators include 'Clock is unsynchronized', 'stratum 16' (which means unsynchronized), or a high offset value. The command is also useful for detecting NTP authentication issues: if authentication is configured but failing, the device may show 'unsynchronized' even if reachable servers exist. In summary, 'show ntp status' is the go-to command for a quick health check of NTP on a Cisco device, providing essential information for troubleshooting time-related issues and ensuring network-wide time accuracy.
show ntp statusWhen to Use This Command
- Verify that a router is synchronized to an NTP server after initial configuration.
- Troubleshoot clock drift or unsynchronized state causing authentication or logging issues.
- Check stratum level to ensure the device is not using a high-stratum (less accurate) reference.
- Confirm NTP association with a specific server after network changes.
Command Examples
Synchronized NTP Status
show ntp statusClock is synchronized, stratum 2, reference is 192.168.1.10 nominal freq is 250.0000 Hz, actual freq is 249.9999 Hz, precision is 2**18 ntp uptime is 1234567 (1/100 of seconds), resolution is 4000 reference time is D3A1B2C4.12345678 (14:30:00.123 UTC Mon Jan 15 2024) clock offset is 0.1234 msec, root delay is 10.5678 msec root dispersion is 5.4321 msec, peer dispersion is 2.3456 msec loopfilter state is 'PHASE' (LOCKED)
Clock is synchronized: device is synced to an NTP source. stratum 2: device is two hops from a stratum 1 clock. reference is 192.168.1.10: IP of the NTP server. nominal/actual freq: oscillator frequency, small deviation is normal. ntp uptime: time since NTP started (in 1/100 sec). reference time: last sync timestamp. clock offset: time difference to server (should be low). root delay/dispersion: network delay and jitter to primary source. loopfilter state: 'LOCKED' indicates stable sync.
Unsynchronized NTP Status
show ntp statusClock is unsynchronized, stratum 16, no reference clock nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**18 ntp uptime is 0, resolution is 4000 reference time is 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 2000) clock offset is 0.0000 msec, root delay is 0.0000 msec root dispersion is 0.0000 msec, peer dispersion is 0.0000 msec loopfilter state is 'SPIK' (UNSYNC)
Clock is unsynchronized: device not synced to any NTP source. stratum 16: indicates unsynchronized (max value). no reference clock: no server reachable. ntp uptime 0: NTP process not running or just started. reference time all zeros: no sync timestamp. clock offset zero: no measurement. loopfilter state 'SPIK' (UNSYNC): indicates no synchronization.
Understanding the Output
The 'show ntp status' output provides a snapshot of the NTP synchronization state. The first line is critical: 'Clock is synchronized' or 'unsynchronized'. Stratum indicates accuracy (1 is most accurate, 16 means unsynchronized).
'reference is' shows the IP of the NTP server used. 'clock offset' should be low (milliseconds) for good sync; high offset indicates delay or drift. 'root delay' and 'root dispersion' reflect network path quality; high values suggest network issues.
'loopfilter state' shows the phase-locked loop status: 'LOCKED' is good, 'SPIK' or 'UNSYNC' indicates problems. In a real network, check that stratum is not 16, offset is under a few milliseconds, and loopfilter is locked.
Configuration Scenarios
Verify NTP synchronization after configuring a single NTP server
A network engineer has configured a Cisco router to synchronize its clock with an internal NTP server at 10.0.0.1. After applying the configuration, they need to verify that the router is synchronized and check the stratum level.
Topology
R1(Gi0/0)---10.0.0.0/24---(Gi0/0)NTP_Server(10.0.0.1)Steps
- 1.Step 1: Enter privileged EXEC mode: Router> enable
- 2.Step 2: Verify NTP associations are present: Router# show ntp associations
- 3.Step 3: Check NTP synchronization status: Router# show ntp status
- 4.Step 4: Examine the output for 'Clock is synchronized', stratum value, and reference clock IP.
! NTP configuration on R1 Router(config)# ntp server 10.0.0.1 Router(config)# end
Verify: Router# show ntp status Clock is synchronized, stratum 2, reference is 10.0.0.1 nominal freq is 250.0000 Hz, actual freq is 249.9990 Hz, precision is 2**19 reference time is D6C8E9A0.12345678 (12:34:56.789 UTC Mon Jan 1 2024) clock offset is 0.1234 msec, root delay is 1.23 msec root dispersion is 2.34 msec, peer dispersion is 0.56 msec loopfilter state is 'CTRL' (Normal), drift is 0.000001234 seconds/sec
Watch out: If the output shows 'Clock is unsynchronized, stratum 16', it means the router has not yet synchronized with the server. This can happen if the NTP server is unreachable, NTP authentication is misconfigured, or the server's stratum is higher than the router's configured max stratum. Wait a few minutes and re-check; if it persists, verify connectivity and NTP server configuration.
Troubleshoot NTP synchronization failure with multiple servers
A router is configured with multiple NTP servers for redundancy, but the clock remains unsynchronized. The engineer uses 'show ntp status' to diagnose the issue and correlate with 'show ntp associations'.
Topology
R1(Gi0/0)---192.168.1.0/24---(Gi0/0)NTP_Server1(192.168.1.10)
R1(Gi0/1)---192.168.2.0/24---(Gi0/0)NTP_Server2(192.168.2.20)Steps
- 1.Step 1: Enter privileged EXEC mode: Router> enable
- 2.Step 2: Check NTP status: Router# show ntp status
- 3.Step 3: If unsynchronized, check associations: Router# show ntp associations
- 4.Step 4: Check association details: Router# show ntp associations detail
- 5.Step 5: Verify reachability to NTP servers using ping or extended ping.
- 6.Step 6: Check for NTP authentication issues: Router# show ntp authentication-status
! NTP configuration on R1 Router(config)# ntp server 192.168.1.10 Router(config)# ntp server 192.168.2.20 prefer Router(config)# ntp authenticate Router(config)# ntp authentication-key 1 md5 CourseivaKey Router(config)# ntp trusted-key 1 Router(config)# end
Verify: Router# show ntp status Clock is unsynchronized, stratum 16, no reference clock nominal freq is 250.0000 Hz, actual freq is 249.9990 Hz, precision is 2**19 reference time is D6C8E9A0.12345678 (12:34:56.789 UTC Mon Jan 1 2024) clock offset is 0.0000 msec, root delay is 0.00 msec root dispersion is 0.00 msec, peer dispersion is 0.00 msec loopfilter state is 'CTRL' (Normal), drift is 0.000000000 seconds/sec Router# show ntp associations address ref clock st when poll reach delay offset disp *~192.168.1.10 .GPS. 1 47 64 1 1.234 0.567 0.890 +~192.168.2.20 .GPS. 1 23 64 1 2.345 1.234 1.456 * master (synced), # master (unsynced), + selected, - candidate, ~ configured Router# show ntp associations detail 192.168.1.10 configured, our_mode client, his_mode server, stratum 1 ... 192.168.2.20 configured, our_mode client, his_mode server, stratum 1 ...
Watch out: Even if associations show reachable servers (reach value > 0), the clock may remain unsynchronized if NTP authentication is failing. In the example, the status shows unsynchronized despite reachable servers. Check 'show ntp authentication-status' to see if authentication keys are valid. Also, ensure the NTP server's key matches the router's key. Another common mistake is forgetting to configure 'ntp trusted-key' for the key used.
Troubleshooting with This Command
When troubleshooting NTP issues, 'show ntp status' is the first command to run. A healthy output shows 'Clock is synchronized' followed by a stratum number (typically 1-15) and a reference IP address. The clock offset should be low (ideally under 100 ms), and root delay/dispersion values should be small.
If the output shows 'Clock is unsynchronized, stratum 16', the device has not synchronized to any NTP source. This is the most common problem indicator. Stratum 16 is a special value meaning 'unsynchronized'.
The reference clock field will show 'no reference clock' or an IP address that is not reachable. The next step is to run 'show ntp associations' to see which servers are configured and their reachability. Look at the 'reach' column: a value of 0 means the server has not been reachable in the last 8 polls; values like 1, 3, 7, 15, 31, 63, 127, 255 indicate increasing reachability (binary shift register).
If reach is 0, check network connectivity (ping, ACLs, routing). If reach is non-zero but the clock is still unsynchronized, check the 'st' (stratum) column: if the server's stratum is 16, the server itself is unsynchronized. Also check the 'delay' and 'offset' values: high delay or offset may indicate network congestion or asymmetric paths.
Another key field is 'disp' (dispersion), which measures the error bound; high dispersion suggests unstable synchronization. If NTP authentication is configured, use 'show ntp authentication-status' to verify that the router has a valid trusted key and that the server's key matches. A common symptom is that 'show ntp associations' shows the server with a '*' (selected) or '+' (candidate) but the clock remains unsynchronized; this often points to authentication mismatch.
Also check the system clock manually with 'show clock' to see if it's wildly off; NTP will not synchronize if the offset is too large (by default, more than 1000 seconds) unless 'ntp update-calendar' is configured or the clock is manually set close. In such cases, manually set the clock approximately before enabling NTP. Another useful command is 'debug ntp all' (use with caution in production) to see NTP packets.
Correlate 'show ntp status' with 'show ntp associations detail' to see the reference clock ID and stratum of each server. If the device is a stratum 1 server itself (e.g., with a GPS reference), 'show ntp status' will show 'reference is .GPS.' or similar. For NTP peers, the output may show 'peer mode' instead of 'client'.
Finally, remember that NTP synchronization can take several minutes (typically 5-10 minutes) after configuration; be patient. If after 15 minutes the clock is still unsynchronized, proceed with the diagnostic flow: check connectivity, authentication, server stratum, and local clock offset.
CCNA Exam Tips
CCNA exam tip: Stratum 16 means the device is not synchronized; this is a common distractor.
CCNA exam tip: The 'reference is' field shows the NTP server IP, not the peer IP in 'show ntp associations'.
CCNA exam tip: A high 'clock offset' (e.g., >1000 msec) indicates NTP is not working properly.
CCNA exam tip: Remember that 'show ntp status' only shows the active reference, while 'show ntp associations' shows all configured servers.
Common Mistakes
Mistake 1: Assuming stratum 16 means the device is a stratum 16 server; it actually means unsynchronized.
Mistake 2: Confusing 'reference is' with the local clock; it's the IP of the NTP server the device is synced to.
Mistake 3: Ignoring 'loopfilter state' — a 'SPIK' state indicates instability even if 'synchronized' is shown.
show ntp status vs show ntp associations
Both 'show ntp status' and 'show ntp associations' are used to diagnose NTP operation, but they provide different views: 'status' focuses on the local clock synchronization state, while 'associations' lists all configured NTP peers/servers and their status.
| Aspect | show ntp status | show ntp associations |
|---|---|---|
| Scope | Local clock synchronization status | Configured NTP peers/servers |
| Key Output | Stratum, reference clock, sync state, root dispersion | Address, reach, mode, stratum, poll, delay, offset, jitter |
| Dependencies | Requires active synchronization; may show 'unsynchronized' | Always displays configured associations, even if unreachable |
| Troubleshooting | Check if device clock is synchronized and accurate | Check connectivity and health of each NTP source |
| Output Format | Single block of text | Table with one row per association |
Use show ntp status when you need to verify if the device's clock is synchronized, the current stratum level, and the identity of the reference clock.
Use show ntp associations when you need to check the status of all configured NTP peers/servers, including reachability, offsets, and jitter.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 switches, ISR 4000 routers), the 'show ntp status' command syntax and output are largely identical to classic IOS. However, IOS-XE may include additional fields like 'clock source' or 'VLAN' in some versions. For example, on Catalyst 9300 running IOS-XE 16.x, the output may show 'Clock is synchronized, stratum 2, reference is 10.0.0.1, clock source is NTP'.
There are no significant syntax differences. In NX-OS (Cisco Nexus switches), the equivalent command is 'show ntp status' as well, but the output format is different. NX-OS displays fields like 'Clock state: synchronized', 'Stratum: 2', 'Reference clock: 10.0.0.1', and includes 'Vrf: default' if VRF-aware.
NX-OS also supports 'show ntp peers' and 'show ntp statistics' for more detail. For ASA firewalls, the command is 'show ntp status' in ASA 8.4(2)+, but earlier versions may use 'show ntp' or 'show ntp associations'. ASA output includes 'Clock is synchronized' and stratum, but the reference clock may show the server IP.
In IOS-XR (Cisco ASR 9000, NCS 5500), the command is 'show ntp status' as well, but the output is more verbose and includes 'NTP state: synchronized', 'Stratum: 2', 'Reference clock: 10.0.0.1', and 'System clock offset'. IOS-XR also requires the 'ntp' process to be running; use 'show ntp associations' for peer details. Note that in some older IOS versions (12.x), the output may not include 'loopfilter state' or 'drift' fields.
In 15.x and later, these are standard. Also, in IOS 12.x, the 'reference time' field uses a different timestamp format. Always check the specific platform documentation for exact field names.
Related Commands
ntp server [ip]
Configures the router to synchronize its system clock with an NTP server, ensuring accurate time for logging, authentication, and network protocols.
show clock
Displays the current system date, time, timezone, and whether the time is synchronized via NTP or manually set, used to verify system time accuracy for logging, authentication, and scheduled tasks.
show ntp associations
Displays the status of NTP associations configured on the device, used to verify NTP synchronization and identify time sources.
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