PCNSE Deploy and Configure Firewalls Practice Question
A security administrator is deploying a PA-5220 firewall with a single external zone and several internal zones. The requirement is to allow DNS queries to any external DNS server while ensuring that responses are permitted only when they match an existing session. Which security policy configuration meets this requirement?
⚠ Common exam trap
The trap here is assuming that return traffic needs an explicit inbound security rule, which would unnecessarily expose the internal network and violate stateful firewall principles.
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 from the internal zones to the external zone with application 'dns' and service 'application-default'. No other rules are needed because the firewall automatically allows return traffic.
The correct configuration allows DNS queries from internal to external zones using the application 'dns' and service 'application-default'. The firewall's stateful nature automatically permits return traffic for established sessions, so no inbound rule is required. Specifying the application ensures only DNS traffic is allowed, and application-default service restricts to standard DNS ports, maintaining security.
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 from the internal zones to the external zone with application 'dns' and service 'application-default'. No other rules are needed because the firewall automatically allows return traffic.
Why this is correct
This rule permits DNS queries from internal zones to any external DNS server. Using application 'dns' with service 'application-default' ensures the correct ports (UDP/TCP 53) are allowed. The firewall's stateful inspection automatically allows return traffic for established sessions, so no separate inbound rule is required. This is the standard best practice for outbound DNS.
- ✗
Create two security rules: one from internal zones to external zone allowing application 'dns', and another from external zone to internal zones allowing application 'dns' to permit responses.
Why it's wrong here
This configuration is unnecessary and insecure. The firewall is stateful; return traffic for an allowed session is automatically permitted without an explicit inbound rule. Adding a rule from external to internal would allow unsolicited DNS queries from the internet, creating a security risk. The second rule is not needed and violates least privilege.
- ✗
Create a security rule from internal zones to external zone with service 'dns' (UDP 53) and application 'any'. This ensures DNS queries are allowed and responses are permitted by the stateful engine.
Why it's wrong here
Using service 'dns' with application 'any' is less secure because it allows any application on UDP port 53, not just DNS. While responses would be permitted, the rule is overly permissive. Best practice is to specify the application 'dns' and use application-default service to ensure only DNS traffic is allowed.
- ✗
Create a security rule from internal zones to external zone with application 'dns' and service 'any'. The firewall will automatically restrict the service to DNS ports based on the application.
Why it's wrong here
Setting service to 'any' does not restrict the service to DNS ports; it allows the application to use any port. While the application 'dns' will identify DNS traffic, the rule would also permit other traffic on non-standard ports if it matches the application signature. This is less secure and not recommended.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Palo Alto Networks exam blueprint
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.