- A
DHCP
Why wrong: DHCP assigns IP addresses, not time.
- B
DNS
Why wrong: DNS resolves names, not time.
- C
NTP
NTP synchronizes system clocks, preventing time-related authentication issues.
- D
RADIUS
Why wrong: RADIUS provides authentication but doesn't manage time.
Question 722 of 1,020
NTP Time Synchronization for Active Directory Authentication
This 220-1201 practice question tests your understanding of network services. 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.
A user reports that their computer's clock is consistently off by several minutes, causing authentication failures with the domain. The network uses Active Directory. Which service should be checked first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Quick Answer
The answer is NTP, or Network Time Protocol, because time synchronization is a foundational requirement for Active Directory authentication. Active Directory relies on Kerberos, which uses time stamps to prevent replay attacks; if a computer’s clock drifts by more than five minutes from the domain controller, authentication will fail. On the CompTIA A+ Core 1 220-1201 exam, this concept tests your understanding that NTP keeps all devices on the network synchronized, and a common trap is to suspect DNS or credential issues first when the real culprit is clock drift. Remember the five-minute rule: Kerberos tolerates a maximum time skew of five minutes, so if a user’s clock is off by several minutes, NTP is the service to check immediately. A helpful memory tip is “NTP keeps the time, Kerberos keeps the trust.”
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
✓
NTP
NTP (Network Time Protocol) is the correct service to check first because the symptom—a clock consistently off by several minutes causing authentication failures with an Active Directory domain—is a classic sign of time synchronization issues. Active Directory uses Kerberos for authentication, which requires the client and domain controller clocks to be within a default skew of 5 minutes (RFC 4120). If the time is off, Kerberos tickets are rejected, leading to authentication failures.
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.
- ✗
DHCP
Why it's wrong here
DHCP assigns IP addresses, not time.
- ✗
DNS
Why it's wrong here
DNS resolves names, not time.
- ✓
NTP
Why this is correct
NTP synchronizes system clocks, preventing time-related authentication issues.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
RADIUS
Why it's wrong here
RADIUS provides authentication but doesn't manage time.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse time synchronization with DHCP or DNS, assuming those services handle all network configuration, but NTP is the root cause for Kerberos authentication failures due to time skew.
Detailed technical explanation
How to think about this question
Under the hood, Windows domain members synchronize time with the domain controller holding the PDC (Primary Domain Controller) emulator FSMO role, which itself syncs with an external NTP source. The Kerberos protocol uses timestamps to prevent replay attacks, and if the client's clock differs from the KDC (Key Distribution Center) by more than the default 5-minute skew, the AS-REQ (Authentication Service Request) is rejected with a KRB_AP_ERR_SKEW error. In real-world scenarios, a misconfigured NTP client or a failing CMOS battery can cause gradual drift, while a firewall blocking UDP port 123 can prevent NTP synchronization entirely.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Network Services — This question tests Network Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: NTP — NTP (Network Time Protocol) is the correct service to check first because the symptom—a clock consistently off by several minutes causing authentication failures with an Active Directory domain—is a classic sign of time synchronization issues. Active Directory uses Kerberos for authentication, which requires the client and domain controller clocks to be within a default skew of 5 minutes (RFC 4120). If the time is off, Kerberos tickets are rejected, leading to authentication failures.
What should I do if I get this 220-1201 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: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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