- A
The VPN server's IP address has changed.
Why wrong: If the IP changed, no one would connect, but others are successful.
- B
The RADIUS server is not reachable from the VPN server.
Why wrong: If unreachable, all users would fail, not just the new one.
- C
The new employee's account is not configured in the RADIUS database.
RADIUS authenticates against its user database; a missing account prevents that user's login.
- D
The DNS server is not resolving the VPN server's hostname.
Why wrong: DNS issues would affect all users trying to connect by hostname, not just one.
Question 67 of 1,020
VPN RADIUS Authentication: User Account Issue
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 technician is troubleshooting why a new employee cannot log into the company's VPN. The VPN uses RADIUS for authentication. Other employees can connect successfully. Which is the most likely cause?
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.
Quick Answer
The answer is that the new employee’s account is not configured in the RADIUS database. This is the most likely cause because RADIUS (Remote Authentication Dial-In User Service) acts as a central authentication server for network services like VPN; when a user attempts to log in, the VPN gateway forwards the credentials to the RADIUS server, which checks them against its own user database. If the account is missing or misconfigured there, authentication fails for that individual while other employees, whose accounts are already in the database, connect without issue. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of how RADIUS decouples authentication from the VPN device itself—a common trap is assuming the problem lies with the VPN gateway or client software, when the real issue is a missing user entry in the central RADIUS store. Remember the memory tip: “RADIUS is the gatekeeper’s list; if the name isn’t on the list, the gate stays shut.”
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 new employee's account is not configured in the RADIUS database.
Since other employees can connect successfully, the VPN server, RADIUS server, and network connectivity between them are functional. The issue is isolated to the new employee, making it most likely that their account has not been added to the RADIUS database. RADIUS authenticates users against a local or directory-based user store; if the account is missing, authentication will fail for that user alone.
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 VPN server's IP address has changed.
Why it's wrong here
If the IP changed, no one would connect, but others are successful.
- ✗
The RADIUS server is not reachable from the VPN server.
Why it's wrong here
If unreachable, all users would fail, not just the new one.
- ✓
The new employee's account is not configured in the RADIUS database.
Why this is correct
RADIUS authenticates against its user database; a missing account prevents that user's login.
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 DNS server is not resolving the VPN server's hostname.
Why it's wrong here
DNS issues would affect all users trying to connect by hostname, not just one.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The key point is that a centralized authentication failure affecting only one user points to a missing or misconfigured user account in the authentication database, not a network or server-wide issue.
Detailed technical explanation
How to think about this question
RADIUS (RFC 2865) uses UDP ports 1812 for authentication and 1813 for accounting. The VPN server acts as a RADIUS client, forwarding credentials to the RADIUS server. If the user object is missing from the RADIUS user database (e.g., in Active Directory or a local users file), the server returns an Access-Reject packet, causing the VPN connection to fail. This is distinct from a server unreachable scenario, which would produce an Access-Timeout or no response.
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.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
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: The new employee's account is not configured in the RADIUS database. — Since other employees can connect successfully, the VPN server, RADIUS server, and network connectivity between them are functional. The issue is isolated to the new employee, making it most likely that their account has not been added to the RADIUS database. RADIUS authenticates users against a local or directory-based user store; if the account is missing, authentication will fail for that user alone.
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: "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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Last reviewed: Jul 4, 2026
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