The answer is a missing route or firewall blocking UDP port 123. NTP synchronization relies entirely on UDP port 123 for communication between the client and server; if the router at 192.168.1.10 is unreachable on that port, the `show ntp status` command will consistently display the clock as unsynchronized, regardless of the NTP configuration being correct. On the CCNA 200-301 v2 exam, this scenario tests your understanding of the NTP transport layer and common Layer 3/4 connectivity issues—a classic trap is assuming the NTP process is misconfigured when the real problem is a blocked port or missing route. Remember the memory tip: “NTP needs a clear path on 123 to keep time from going askew.”
CCNA AI and Network Operations Practice Question
This 200-301 practice question tests your understanding of ai and network operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Router# show ntp status
Clock is synchronized, stratum 16, reference is 0.0.0.0
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**10
reference time is 0.0.0.0
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 0.00 msec, peer dispersion is 0.00 msec
Router# show ntp associations
address ref clock st when poll reach delay offset disp
*~192.168.1.10 .INIT. 16 - 64 0 0.0 0.00 16000.
* sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
Router# show running-config | include ntp
ntp server 192.168.1.10
A network engineer notices that the system clock on a Cisco IOS-XE router is incorrect, causing syslog timestamps to be unreliable. The router is configured as an NTP client to synchronize with a remote NTP server at 192.168.1.10. However, the show ntp status command indicates the clock is unsynchronized. What is the most likely cause of this issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Router# show ntp status
Clock is synchronized, stratum 16, reference is 0.0.0.0
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**10
reference time is 0.0.0.0
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 0.00 msec, peer dispersion is 0.00 msec
Router# show ntp associations
address ref clock st when poll reach delay offset disp
*~192.168.1.10 .INIT. 16 - 64 0 0.0 0.00 16000.
* sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
Router# show running-config | include ntp
ntp server 192.168.1.10
A
The NTP server is using TCP instead of UDP for NTP communication.
Why wrong: NTP uses UDP port 123, not TCP. This is a common misconception.
B
The router cannot reach the NTP server due to a missing route or firewall blocking UDP port 123.
The reach value of 0 indicates no NTP packets have been received, typically due to connectivity issues or ACL/firewall blocking UDP 123.
C
The NTP server has a higher stratum level than the router's local clock, so the router ignores it.
Why wrong: NTP synchronization does not require any interactive session like Telnet.
D
NTP authentication is misconfigured on the router.
Why wrong: NTP authentication is not configured in the running-config, and the symptom is a lack of connectivity, not authentication failure.
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 due to a missing route or firewall blocking UDP port 123.
NTP operates over UDP port 123. If the router cannot reach the NTP server at 192.168.1.10 due to a missing route or a firewall blocking UDP 123, the NTP client will remain unsynchronized, as indicated by the 'show ntp status' command showing the clock as unsynchronized. This is the most common cause of NTP synchronization failure in a network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 server is using TCP instead of UDP for NTP communication.
Why it's wrong here
NTP uses UDP port 123, not TCP. This is a common misconception.
✓
The router cannot reach the NTP server due to a missing route or firewall blocking UDP port 123.
Why this is correct
The reach value of 0 indicates no NTP packets have been received, typically due to connectivity issues or ACL/firewall blocking UDP 123.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The NTP server has a higher stratum level than the router's local clock, so the router ignores it.
Why it's wrong here
NTP synchronization does not require any interactive session like Telnet.
✗
NTP authentication is misconfigured on the router.
Why it's wrong here
NTP authentication is not configured in the running-config, and the symptom is a lack of connectivity, not authentication failure.
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 due to a missing route or firewall blocking UDP port 123.Correct answer▾
Why this is correct
The reach value of 0 indicates no NTP packets have been received, typically due to connectivity issues or ACL/firewall blocking UDP 123.
✗The NTP server is using TCP instead of UDP for NTP communication.Wrong answer — click to see why▾
Why this is wrong here
NTP exclusively uses UDP port 123 for communication, not TCP. The statement that NTP uses TCP is factually incorrect.
Why candidates choose this
Students may confuse NTP with other protocols that use TCP, such as SNMP or FTP, or may recall that some NTP implementations can use TCP for control messages, but standard NTP synchronization uses UDP.
✗The NTP server has a higher stratum level than the router's local clock, so the router ignores it.Wrong answer — click to see why▾
Why this is wrong here
The router synchronizes with the server as long as the server's stratum is lower (more accurate) than the local clock; if the server has a higher stratum, the router may still synchronize if the local clock is unsynchronized, but this is not the most likely cause of the 'unsynchronized' state.
Why candidates choose this
A student might think that because Telnet is used for remote management, it might be needed to initiate NTP synchronization, or they may confuse NTP with other protocols that require a session.
✗NTP authentication is misconfigured on the router.Wrong answer — click to see why▾
Why this is wrong here
NTP authentication is not configured in the running-config, and the symptom described (unsynchronized clock with reach value 0) indicates a lack of connectivity, not an authentication failure. Authentication issues would typically show NTP packets being received but rejected, resulting in a non-zero reach value.
Why candidates choose this
Students may know that NTP authentication can cause synchronization issues if misconfigured, and might assume that any NTP problem is due to authentication, especially if they have studied NTP authentication scenarios.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that NTP uses TCP or that authentication is the primary cause of synchronization failure, when in fact the most common issue is simple network reachability or firewall blocking of UDP port 123.
Detailed technical explanation
How to think about this question
NTP relies on UDP port 123 to minimize latency and avoid the overhead of TCP's connection establishment and retransmission, which would degrade time accuracy. When a router is configured as an NTP client, it sends NTP packets to the server and expects replies; if the server is unreachable, the NTP process will never receive a valid timestamp, leaving the clock in an unsynchronized state. In real-world scenarios, administrators often overlook firewall rules or ACLs that block UDP 123, especially when the NTP server is on a different subnet or behind a firewall.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
AI and Network Operations — This question tests AI and Network Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The router cannot reach the NTP server due to a missing route or firewall blocking UDP port 123. — NTP operates over UDP port 123. If the router cannot reach the NTP server at 192.168.1.10 due to a missing route or a firewall blocking UDP 123, the NTP client will remain unsynchronized, as indicated by the 'show ntp status' command showing the clock as unsynchronized. This is the most common cause of NTP synchronization failure in a network.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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