Interzone Rule Not Matching: Earlier Deny Rule
An engineer is troubleshooting an inter-zone rule that should allow traffic from zone 'Trust' to zone 'Untrust'. The rule has a source address of 10.0.0.0/8 and destination address of any. The traffic is being denied. The engineer checks the log and sees the rule is not matched. What is the most likely reason?
Quick Answer
The answer is that a rule with a 'deny' action appearing earlier in the security policy is the most likely reason the interzone rule is not matched. This occurs because Palo Alto Networks firewalls evaluate security rules sequentially from top to bottom, and the first matching rule determines the action for the traffic. If an earlier deny rule matches the source, destination, or application before the intended allow rule is reached, the later rule is never evaluated, resulting in the interzone rule not matching earlier deny rule behavior. On the PCNSE exam, this concept tests your understanding of rule order and policy evaluation logic, often appearing in troubleshooting scenarios where traffic is unexpectedly denied despite a seemingly correct allow rule. A common trap is assuming a broader allow rule will override a specific deny rule placed above it. Remember the memory tip: "First match wins, so order your denies before your allows."
⚠ Common exam trap
Candidates often assume the rule itself is misconfigured (e.g., source or destination issues) rather than recognizing that a higher-priority deny rule is preempting the intended allow rule.
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
✓
A rule with a 'deny' action appears earlier in the security policy.
The most likely reason the inter-zone rule is not matched is that a preceding rule with a 'deny' action is matching the traffic first. In Palo Alto Networks firewalls, security rules are evaluated in order from top to bottom, and the first matching rule determines the action. If an earlier rule denies the traffic, the later allow rule will never be evaluated, even if it would otherwise match.
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 address 10.0.0.0/8 is not included in the source zone.
Why it's wrong here
A rule matches only when the source IP falls within the source zone's bound interfaces; 10.0.0.0/8 traffic arriving on an interface assigned to another zone never reaches this rule. Zone membership is tempting because the address looks internal, and would be correct had the subnet been bound to the Trust zone.
- ✗
The destination address is set to 'any', which is not valid.
Why it's wrong here
'Any' is a valid destination value in PAN-OS security policy, so this cannot explain the non-match. It is tempting because overly broad rules are poor practise, but 'any' is genuinely used when a rule should cover all destinations, and the mismatch lies elsewhere.
- ✗
The traffic is intra-zone, not inter-zone.
Why it's wrong here
Intra-zone traffic never traverses an inter-zone rule, so the rule cannot match regardless of its addresses; the log would show the intra-zone default action instead. It is tempting because intra-zone rules do exist, but those apply only when source and destination interfaces sit in the same zone.
- ✓
A rule with a 'deny' action appears earlier in the security policy.
Why this is correct
Palo Alto Networks evaluates security policy top-down and stops at the first matching rule. A deny rule positioned above the intended allow rule matches the traffic first, so the allow rule never appears in the log as a hit, explaining the observed denial.
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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. A network engineer is configuring a new firewall to replace an existing one. The existing firewall has a policy that allows traffic from the 10.0.0.0/8 subnet to the internet. The new firewall must use the same policy but also log the traffic. The engineer creates a security rule with source zone 'Trust', destination zone 'Untrust', source address 10.0.0.0/8, and action 'allow'. Logging is set at rule end. However, traffic from 10.1.0.0/16 is not being logged. What is the reason?
hard- ✓ A.Another rule earlier in the policy matches the traffic and allows it before reaching this rule.
- B.The firewall is configured to not log interzone traffic.
- C.The source address 10.1.0.0/16 is not part of the 10.0.0.0/8 subnet.
- D.The logging profile is not applied to the rule.
Why A: In a Palo Alto Networks firewall, security rules are evaluated from top to bottom, and the first matching rule is applied. If an earlier rule in the policy matches the traffic from 10.1.0.0/16 and allows it, the rule with logging at rule end will never be evaluated, and thus no log entry is generated for that traffic.
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.