Security Policy Deny Despite Allow Rule: Rulebase and Zone Specificity
Exhibit
show session id 12345 Session 12345: 10.1.1.10:50000 -> 203.0.113.5:443 (10.1.1.10:50000 -> 203.0.113.5:443) Application: ssl State: DROP Type: FLOW Reason: policy-deny Flags: 0x40000000 NAT: source 10.1.1.10:50000 (no NAT)
Refer to the exhibit. A user at 10.1.1.10 is trying to connect to a web server at 203.0.113.5 on port 443. The session shows 'State: DROP' with reason 'policy-deny'. However, the administrator has a security policy rule that allows SSL traffic from the source zone to the destination zone. What is the most likely cause of the drop?
Quick Answer
The correct answer is that the allow rule exists somewhere the traffic never actually reaches, and understanding why requires remembering how the firewall evaluates policy: rules are checked in a strict order across the pre-rulebase, the main rulebase, and the post-rulebase, and only for the specific source-zone-to-destination-zone pair the traffic is actually crossing. A rule that looks correct in isolation does nothing if it sits in the wrong rulebase for that device's role, or if it is written for a different zone pair than the one the session is actually traversing. A 'policy-deny' result with a DROP state means the firewall reached the end of its evaluation without a match, whether because an earlier rule caught the traffic first or because the intended allow rule was simply never in scope. This is a different failure mode than a misconfigured rule that is present and evaluated but written too narrowly, since here the administrator's rule is correct in content but wrong in placement or zone context. Whenever you see a policy-deny drop despite an administrator insisting a matching allow rule exists, the fix is rarely to rewrite the rule's match criteria; it's to verify the rule actually sits in the rulebase and zone pair the traffic is passing through.
⚠ Common exam trap
It's easy for candidates to assume a security policy rule exists globally, but the PCNSE exam tests the understanding that rules are zone-specific and rulebase-specific, so a rule in the wrong zone pair or rulebase will not be matched, leading to a policy-deny drop.
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 security policy rule that allows SSL is in a different rulebase or zone than the traffic.
The session shows 'policy-deny' with a DROP state, which indicates that the traffic matched a deny rule or did not match any allow rule in the security policy. Even though the administrator believes an SSL allow rule exists, the most common cause is that the rule is in a different rulebase (e.g., pre-rulebase or post-rulebase) or the traffic is traversing a different zone pair than the one the rule applies to. The firewall evaluates rules in a specific order (pre-rulebase, then rulebase, then post-rulebase), and if the rule is not in the correct location for the traffic's ingress and egress zones, it will not be matched, resulting in a policy-deny drop.
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 source NAT rule is missing, so the private IP cannot reach the internet.
Why it's wrong here
A missing NAT rule would cause the session to not be established, but the drop reason explicitly says 'policy-deny', not 'no-route' or 'nat-fail'.
- ✓
The security policy rule that allows SSL is in a different rulebase or zone than the traffic.
Why this is correct
The traffic may be matched by an earlier deny rule or the zone context might be wrong.
- ✗
The SSL application is not correctly identified because the traffic is encrypted.
Why it's wrong here
SSL is correctly identified as the application; the issue is policy-based.
- ✗
The firewall is configured to block SSL sessions that use weak ciphers.
Why it's wrong here
This would result in a different session end reason, such as 'decryption-error'.
Go deeper
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Same concept, more angles
2 more ways 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. The traffic log shows a drop event from source IP 203.0.113.10 to destination 10.1.1.200 on port 443. The rule matched is 'deny-rule'. What is the most likely reason for this drop?
hard- ✓ A.The traffic matched a security rule that explicitly denies it
- B.A threat prevention profile detected and blocked the session
- C.The traffic was blocked because the application is not allowed
- D.The destination URL is categorized as prohibited
Why A: The traffic log explicitly states that the rule matched is 'deny-rule'. In Palo Alto Networks firewalls, when a security rule is configured with an action of 'Deny', any traffic matching that rule is dropped and logged with a 'deny' action. Since the log shows a drop event and the matched rule is 'deny-rule', the most direct and likely reason is that the traffic was explicitly denied by this security rule, not by any additional security profiles or external factors.
Variation 2. A network engineer notices that traffic from a specific subnet is being dropped by the firewall. The traffic log shows 'drop' with reason 'policy deny'. The engineer checks the security policy and confirms there is an allow rule for that subnet. What should be checked next?
easy- A.Check the application override.
- B.Check the QoS policy.
- ✓ C.Check the rule order and ensure the allow rule is above any deny rules.
- D.Check the NAT policy for the traffic.
Why C: When a traffic log shows 'policy deny' despite an existing allow rule, the most common cause is rule order: Palo Alto firewalls evaluate security rules from top to bottom, and the first matching rule is applied. If a deny rule appears above the allow rule for the same subnet, the deny rule will match first and drop the traffic, making it essential to verify the rule sequence.
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.