Question 1,113 of 1,389
CCNA Network Services and Security Practice Question
Exhibit
R1# show ntp status Clock 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 15000 (4.1 hours) reference time is 00000000.00000000 (00:00:00.000 UTC Jan 1 1900) 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 Controlled Loop), drift is 0.000000000 s/s system poll interval is 64, last update was 0 sec ago.
Refer to the exhibit. A network administrator is troubleshooting an NTP synchronization issue on R1. The router is configured with the command ntp server 10.1.1.100, but the clock remains unsynchronized. The administrator issues the show ntp status command. What is the most likely cause of the problem?
⚠ Common exam trap
Cisco often tests the misconception that the `ntp server` command alone is insufficient and that an additional 'ntp enable' command is needed, but in reality, the client process is automatically started by the `ntp server` command.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The router cannot reach the NTP server 10.1.1.100 at UDP port 123 due to a routing issue or an access list.
The `show ntp status` output would show the clock as unsynchronized if R1 cannot communicate with the NTP server at 10.1.1.100. NTP uses UDP port 123, and a routing issue or an access list blocking this port would prevent the exchange of NTP packets, leaving the clock unsynchronized. The `ntp server` command configures R1 as a client to request synchronization, but it does not guarantee reachability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The NTP authentication key configured on R1 does not match the one on the server.
Why it's wrong here
While an authentication mismatch would prevent synchronization, the router would still receive NTP packets from the server, and show ntp associations would likely show the server as reachable but with a status of 'reject' or 'bad auth.' The exhibit shows no reference clock at all, indicating no NTP packets are arriving.
- ✗
The system time on R1 is set to an epoch that is too far from the server's time, causing NTP to refuse to synchronize.
Why it's wrong here
NTP can handle any time difference, although a very large offset (e.g., >1000 seconds by default) might trigger a panic and require manual stepping. However, in that case, the server would still be reachable and the output might show the server as a candidate but with a large offset; it would not result in 'no reference clock' and a persistent unsynchronized state without any peer communication.
- ✗
The NTP service is not enabled on R1; the 'ntp server' command only defines a server but does not start the NTP process.
Why it's wrong here
The 'ntp server' command indeed enables the NTP service and starts the daemon. If NTP were not enabled, the 'show ntp status' command would return an error or indicate that NTP is not running, rather than showing detailed status fields. The output confirms NTP is running but unsynchronized.
- ✓
The router cannot reach the NTP server 10.1.1.100 at UDP port 123 due to a routing issue or an access list.
Why this is correct
The exhibit clearly shows 'no reference clock' and stratum 16, which indicates that R1 has not received any NTP packets from the configured server. This is a classic symptom of network unreachability—the router’s NTP requests are not making it to the server or responses are not coming back, often caused by a missing route or an ACL filtering UDP 123.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The router cannot reach the NTP server 10.1.1.100 at UDP port 123 due to a routing issue or an access list.Correct answer▾
Why this is correct
The exhibit clearly shows 'no reference clock' and stratum 16, which indicates that R1 has not received any NTP packets from the configured server. This is a classic symptom of network unreachability—the router’s NTP requests are not making it to the server or responses are not coming back, often caused by a missing route or an ACL filtering UDP 123.
✗The NTP authentication key configured on R1 does not match the one on the server.Wrong answer — click to see why▾
Why this is wrong here
Candidates often confuse unsynchronized status with authentication issues, but authentication failures do not prevent reception of packets; they just discard them after arrival.
✗The system time on R1 is set to an epoch that is too far from the server's time, causing NTP to refuse to synchronize.Wrong answer — click to see why▾
Why this is wrong here
A common myth is that NTP cannot sync if the clocks are too far apart. While extreme offsets may delay sync, they do not prevent the router from hearing the server, so the reference clock field would still show the server’s IP or clock ID.
✗The NTP service is not enabled on R1; the 'ntp server' command only defines a server but does not start the NTP process.Wrong answer — click to see why▾
Why this is wrong here
Some candidates mistakenly believe that a separate 'ntp enable' command is required. In IOS, configuring an ntp server automatically enables NTP, so the service is active.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Last reviewed: Jul 4, 2026
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