Palo Alto Networks (PANW) Certified Network Security Administrator (PCNSA) Practice Exam

What happens if a security rule with a deny action covers packets from all sources to all destinations?

1. All traffic is allowed by default

2. Only specific protocols will be denied

3. Traffic is denied based on the active session

4. All traffic will be denied by the rule

The correct answer is: All traffic will be denied by the rule

When a security rule is configured with a deny action that covers all sources to all destinations, it effectively acts as a catch-all rule. This means that any packet traversing the network that matches this rule will be blocked. The rule does not discriminate based on the type of traffic; it simply denies all packets falling within its defined scope. In a typical firewall or security policy framework, the deny action takes precedence over any allow actions. Therefore, once a packet matches the criteria (all sources to all destinations), it will be immediately denied. This is essential for enforcing security measures by preventing unwanted or potentially harmful traffic from entering or leaving the network. Understanding this behavior is crucial, as it establishes the foundation for creating effective security policies. Without having explicit allow rules to permit specific traffic, any traffic not explicitly permitted will fall under the deny action of this rule, leading to total blockage. This principle reinforces the importance of a default-deny posture in network security, aiming to protect against unauthorized access while allowing only necessary communications through specifically defined rules.