NSE4 Authentication and VPN Practice Question
An administrator runs 'diagnose debug application fnbamd -1' on a FortiGate to troubleshoot authentication issues. The output shows that the FortiGate successfully contacts the LDAP server but the user authentication fails. What does this indicate?
⚠ Common exam trap
It's easy for candidates to confuse a successful TCP connection or LDAP server response with successful authentication, not realizing that the FortiGate must perform a separate bind with the user's credentials, which can fail independently.
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 user's password is incorrect or the user account is locked
The 'diagnose debug application fnbamd -1' output shows successful contact with the LDAP server, meaning network connectivity and server reachability are fine. Since the server is reachable but authentication fails, the most likely cause is that the user's credentials (password) are incorrect or the account is locked/disabled on the LDAP server. This is a standard LDAP bind failure scenario where the server returns an 'invalid credentials' or 'account locked' error.
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 user's password is incorrect or the user account is locked
Why this is correct
In the fnbamd debug output, "successful contact" confirms that the FortiGate established a TCP session and communicated with the LDAP server; the failure happens during the final bind step where the end user's distinguished name (DN) and password are verified. An LDAP 'invalidCredentials' or 'accountDisabled' result at this stage is the server's definitive rejection of that specific user's password or account state, not a communication problem. Therefore, the correct interpretation is that the user's password is wrong or the user account is locked out, disabled, or expired.
- ✗
The LDAP server is unreachable
Why it's wrong here
The fnbamd debug log explicitly records "successful contact" with the LDAP server, meaning the FortiGate resolved the server name, reached it over the network, and received a response—likely a connection acknowledgment or an LDAP greeting. If the server were unreachable, the debug output would instead show repeated connection timeouts, 'no response', or a failure to establish a socket, not a successful contact followed by an authentication attempt. Thus, the option is directly contradicted by the evidence in the log.
- ✗
The LDAP bind user password is incorrect
Why it's wrong here
When the LDAP bind user (the service account FortiGate uses to search the directory) has an incorrect password, the initial bind phase fails immediately, preventing any subsequent query or user authentication. The debug output shows that FortiGate not only contacted the server but also proceeded to attempt user authentication, which proves the service account bind succeeded and the server accepted those credentials. A bad bind password would produce an error much earlier in the sequence, before any specific user's credentials are validated.
- ✗
The LDAP schema does not match what FortiGate expects
Why it's wrong here
An LDAP schema mismatch typically surfaces as failures to map directory attributes (for example, missing sAMAccountName, memberOf, or group objects), generating errors like 'attribute not found' or 'cannot retrieve user groups', rather than a clean 'authentication failed' response. The debug output shows the server accepted the user DN and password attempt, which indicates the server could locate the user object and evaluate the credentials; a schema problem would not affect the basic LDAP bind operation that verifies the password. Therefore, schema mismatch does not explain a specific user authentication failure after successful contact.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE4 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE4 exam.