Matching Traffic with Application and Service in Security Rules
This PCNSA practice question tests your understanding of securing traffic. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
Exhibit: CLI output from 'show running security-policy' shows:
```
set rulebase security rules "Allow_Web" from untrust to dmz source any destination 10.1.1.0/24 application web-browsing,ssl service tcp/80, tcp/443 action allow log-end
set rulebase security rules "Block_ALL" from any to any source any destination any application any service any action deny
```
Based on the exhibit, what will happen to an HTTPS request from an untrust zone user to destination IP 10.1.1.50?
Exhibit
Refer to the exhibit.
Exhibit: CLI output from 'show running security-policy' shows:
```
set rulebase security rules "Allow_Web" from untrust to dmz source any destination 10.1.1.0/24 application web-browsing,ssl service tcp/80, tcp/443 action allow log-end
set rulebase security rules "Block_ALL" from any to any source any destination any application any service any action deny
```
A
Denied because the source is not specified in Allow_Web.
Why wrong: The rule specifies source any, so all sources from untrust are matched.
B
Denied by rule Block_ALL because it is the last rule.
Why wrong: The traffic matches the first rule Allow_Web, so it is allowed and never reaches Block_ALL.
C
Allowed by rule Allow_Web because service tcp/443 matches.
HTTPS uses tcp/443, and the rule allows that service along with application ssl.
D
Allowed by rule Allow_Web because application ssl matches.
Why wrong: Although ssl matches, the service tcp/443 also matches and is more explicit in this context.
The correct answer is that the HTTPS request is allowed by the rule Allow_Web because the service tcp/443 matches. This occurs because Palo Alto Networks security rules evaluate traffic by checking both the application and the service object; here, the application ssl matches the HTTPS traffic, and the service object tcp/443 explicitly matches the destination port, so the rule permits the connection. On the PCNSA exam, this scenario tests your understanding of how service objects narrow rule matching beyond just application identification—a common trap is assuming application alone determines the match, but the service object must also align for the rule to apply. Remember that a rule with a specific service like tcp/443 will only match traffic on that exact port, even if the application is correct, so always verify both fields. A helpful memory tip is “App for what, service for where”—the application identifies the protocol, while the service specifies the 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
✓
Allowed by rule Allow_Web because service tcp/443 matches.
Option C is correct. The rule 'Allow_Web' permits traffic matching service tcp/443 from any source. An HTTPS request to 10.1.1.50 uses tcp/443, so it matches the rule and is allowed. Option D is also true because HTTPS corresponds to application ssl, but the rule's service match is explicit; however, the question's intended correct answer is C as it directly references the service match. The previous explanation incorrectly stated that option D was wrong due to source being 'any,' which is not relevant.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Denied because the source is not specified in Allow_Web.
Why it's wrong here
The rule specifies source any, so all sources from untrust are matched.
✗
Denied by rule Block_ALL because it is the last rule.
Why it's wrong here
The traffic matches the first rule Allow_Web, so it is allowed and never reaches Block_ALL.
✓
Allowed by rule Allow_Web because service tcp/443 matches.
Why this is correct
HTTPS uses tcp/443, and the rule allows that service along with application ssl.
Related concept
Standard ACLs match source addresses.
✗
Allowed by rule Allow_Web because application ssl matches.
Why it's wrong here
Although ssl matches, the service tcp/443 also matches and is more explicit in this context.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNSA ACL questions on filtering logic and placement.
Securing Traffic — This question tests Securing Traffic — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Allowed by rule Allow_Web because service tcp/443 matches. — Option C is correct. The rule 'Allow_Web' permits traffic matching service tcp/443 from any source. An HTTPS request to 10.1.1.50 uses tcp/443, so it matches the rule and is allowed. Option D is also true because HTTPS corresponds to application ssl, but the rule's service match is explicit; however, the question's intended correct answer is C as it directly references the service match. The previous explanation incorrectly stated that option D was wrong due to source being 'any,' which is not relevant.
What should I do if I get this PCNSA question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNSA ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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