How to Allow Only Specific Applications and Block All Others with App-ID
A network administrator wants to allow only specific applications such as 'facebook-base' and 'youtube' while blocking all other applications. Which type of security rule should be used to achieve this?
Quick Answer
The answer is to create a security rule with application conditions set to 'facebook-base' and 'youtube' and the action set to 'allow'. This is correct because App-ID enables you to allow only specific applications by explicitly listing them in a rule, while the firewall’s default implicit deny automatically blocks all other traffic that does not match an allow rule. On the PCNSE exam, this tests your understanding of how App-ID rules leverage implicit deny—a common trap is thinking you need a separate block rule, but the default action for unmatched traffic is already deny. The key insight is that you do not need to explicitly block other applications; simply allowing the desired ones achieves the goal. Memory tip: think of it as a “whitelist” approach—only what you name gets through, everything else is stopped by default.
⚠ Common exam trap
Many exam-takers confuse port-based rules (Option B) with application-based rules, assuming that allowing ports 80/443 is sufficient to control application access, but App-ID is required to distinguish between applications using the same port.
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
✓
Create a security rule with application conditions set to 'facebook-base' and 'youtube' and action set to 'allow'.
App-ID allows you to create a security rule that explicitly allows only the specified applications ('facebook-base' and 'youtube') while implicitly denying all other traffic. Since the default action for any traffic not matching an allow rule is 'deny', this rule achieves the goal of blocking all other applications without needing an explicit block rule.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create a security rule with application conditions set to 'facebook-base' and 'youtube' and action set to 'allow'.
Why this is correct
This rule allows only the specified applications.
- ✗
Create a security rule with destination port 80 and 443 and action set to 'allow'.
Why it's wrong here
This would allow all HTTP/HTTPS traffic, not just specific applications.
- ✗
Create a security profile that blocks all applications not in the allow list.
Why it's wrong here
Security profiles apply threats, not application control.
- ✗
Create a URL filtering rule to allow 'social-networking' and 'multimedia' categories.
Why it's wrong here
URL filtering controls web access, not application identification.
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Same concept, more angles
1 more way this is tested on PCNSE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A network engineer wants to allow only 'ms-update' and 'facebook-base' traffic. After committing the above security policy, they find that 'ssl' traffic is also being allowed. What is the most likely reason?
medium- ✓ A.Rule 1 allows all applications because it uses 'application any'.
- B.App-ID is not enabled on the firewall.
- C.Rule 4 is a deny rule but it is not effective because the traffic is allowed earlier.
- D.The rule order is incorrect; rule 3 should be moved before rule 1.
Why A: Rule 1 uses 'application any', which matches all applications regardless of the specific App-ID. Since security policies are evaluated from top to bottom and the first matching rule is applied, any traffic that matches Rule 1's source, destination, and service will be allowed, including 'ssl' traffic. The explicit allow rules for 'ms-update' and 'facebook-base' are irrelevant because Rule 1 catches all traffic first.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNSE practice question is part of Courseiva's free Palo Alto Networks 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 PCNSE exam.