Question 1hardmultiple choice
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Question 164 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Notices that the system clock on a Cisco IOS-XE…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
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 due to a missing route or firewall blocking UDP port 123.
The show ntp status output shows stratum 16, which indicates the router is not synchronized to an authoritative time source. The reference clock is 0.0.0.0, meaning no valid NTP server has been reached. The show ntp associations output shows the configured server with a reach value of 0, indicating that no NTP packets have been received from the server. This typically occurs when the NTP server is unreachable due to a missing default route, ACL blocking NTP (UDP port 123), or a firewall issue. The correct answer is B: verify IP connectivity to the NTP server and ensure UDP port 123 is permitted. Option A is incorrect because NTP uses UDP, not TCP. Option C is incorrect because NTP does not use Telnet or require a Telnet session. Option D is incorrect because NTP authentication is not configured, and the symptom is a lack of connectivity, not an authentication failure.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
- ✓
The router cannot reach the NTP server due to a missing route or firewall blocking UDP port 123.
- ✗
The NTP server requires a Telnet session to synchronize.
- ✗
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 operates over UDP, so TCP would not be used.
✗The NTP server requires a Telnet session to synchronize.Wrong answer — click to see why▾
Why this is wrong here
Telnet is not used for NTP; NTP uses UDP port 123 for time synchronization.
✗NTP authentication is misconfigured on the router.Wrong answer — click to see why▾
Why this is wrong here
NTP authentication would show a different symptom, such as 'authentication failed' in the NTP associations output.
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: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 200-301 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Standard ACLs match source addresses.
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. — The show ntp status output shows stratum 16, which indicates the router is not synchronized to an authoritative time source. The reference clock is 0.0.0.0, meaning no valid NTP server has been reached. The show ntp associations output shows the configured server with a reach value of 0, indicating that no NTP packets have been received from the server. This typically occurs when the NTP server is unreachable due to a missing default route, ACL blocking NTP (UDP port 123), or a firewall issue. The correct answer is B: verify IP connectivity to the NTP server and ensure UDP port 123 is permitted. Option A is incorrect because NTP uses UDP, not TCP. Option C is incorrect because NTP does not use Telnet or require a Telnet session. Option D is incorrect because NTP authentication is not configured, and the symptom is a lack of connectivity, not an authentication failure.
What should I do if I get this 200-301 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 200-301 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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