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SSCP Practice Question: An administrator configures a Kerberos…
An administrator configures a Kerberos authentication system. After implementation, users are able to authenticate but cannot access network resources. The administrator verifies that the client time is synchronized with the KDC. What is the most likely cause?
⚠ Common exam trap
ISC2 often tests the distinction between authentication (TGT acquisition) and authorization (service ticket issuance), leading candidates to incorrectly focus on firewall rules or password expiration instead of the missing SPN.
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 service principal name (SPN) is not registered
The most likely cause is that the service principal name (SPN) is not registered. In Kerberos, the SPN uniquely identifies a network service instance and is required for the KDC to issue a service ticket. Even though users can authenticate (obtain a TGT), without a properly registered SPN, the KDC cannot grant a ticket for the target service, preventing access to network resources.
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 service principal name (SPN) is not registered
Why this is correct
Kerberos authentication succeeds because the ticket-granting service works, but resource access fails when the target service's SPN is absent from the directory, so the KDC cannot issue a service ticket for that resource. Time synchronisation is already verified, ruling out clock skew.
- ✗
The user’s password is expired
Why it's wrong here
An expired password prevents initial authentication, yet the stem states users authenticate successfully, so it cannot explain the resource-access failure. It is tempting because expired passwords commonly block logons, and it would be correct if users could not obtain a ticket-granting ticket at all.
- ✗
The firewall blocks port 88
Why it's wrong here
Blocking port 88 would prevent Kerberos authentication entirely, contradicting the stem's successful authentication. It is tempting because firewall filtering of Kerberos traffic is a frequent cause of failure, and it would be correct if clients could not reach the KDC to obtain tickets.
- ✗
The TGT lifetime has expired
Why it's wrong here
An expired TGT forces re-authentication rather than silently blocking resource access, and clients renew or reacquire tickets automatically. It is tempting because ticket lifetime is a Kerberos concept, and it would be correct if users were prompted repeatedly to authenticate during a session.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SSCP practice question is part of Courseiva's free ISC2 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 SSCP exam.