CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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
ASA1# show conn
21 in use, 52 most used
TCP outside 203.0.113.5:443 inside 10.0.0.10:49152, idle 0:00:02, bytes 10240, flags UIO
UDP outside 198.51.100.2:53 inside 10.0.0.5:12345, idle 0:00:15, bytes 512, flags -
TCP outside 203.0.113.10:80 inside 10.0.0.20:49153, idle 0:00:05, bytes 2048, flags UIO
ASA1# show access-list outside_in
access-list outside_in line 1 extended permit tcp any host 203.0.113.5 eq 443 (hitcnt=0)
access-list outside_in line 2 extended permit udp any host 198.51.100.2 eq 53 (hitcnt=0)
access-list outside_in line 3 extended deny ip any any (hitcnt=0)
Refer to the exhibit. Which of the following statements is correct regarding the connections and access-list?
ASA1# show conn
21 in use, 52 most used
TCP outside 203.0.113.5:443 inside 10.0.0.10:49152, idle 0:00:02, bytes 10240, flags UIO
UDP outside 198.51.100.2:53 inside 10.0.0.5:12345, idle 0:00:15, bytes 512, flags -
TCP outside 203.0.113.10:80 inside 10.0.0.20:49153, idle 0:00:05, bytes 2048, flags UIO
ASA1# show access-list outside_in
access-list outside_in line 1 extended permit tcp any host 203.0.113.5 eq 443 (hitcnt=0)
access-list outside_in line 2 extended permit udp any host 198.51.100.2 eq 53 (hitcnt=0)
access-list outside_in line 3 extended deny ip any any (hitcnt=0)
A
The access-list 'outside_in' is applied to the outside interface and is allowing the connections.
Why wrong: Incorrect. The hit counts are 0, so the access-list is not being used.
B
The UDP connection to 198.51.100.2:53 is being allowed by line 2 of the access-list.
Why wrong: Incorrect. Line 2 has 0 hits, so it is not allowing the traffic.
C
The access-list 'outside_in' is not applied to any interface or is not the primary access-list governing inbound traffic.
Correct. The connections exist but the access-list has 0 hits, implying either it is not applied or another rule is allowing traffic (e.g., an implicit permit for established connections).
D
The TCP connection to 203.0.113.5:443 is being denied by the implicit deny rule.
Why wrong: Incorrect. The connection exists (flags UIO), so it is not denied.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The access-list 'outside_in' is not applied to any interface or is not the primary access-list governing inbound traffic.
The access-list 'outside_in' is applied to the outside interface for inbound traffic. However, the hit counts are all 0, meaning the access-list is not being hit. This suggests that the access-list is not applied to the interface, or the interface has another access-list that allows the traffic, or the connections are established through other means (like stateful inspection). The connections are active, so traffic is passing through the ASA. The access-list with 0 hits indicates it is not the mechanism allowing the traffic.
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.
✗
The access-list 'outside_in' is applied to the outside interface and is allowing the connections.
Why it's wrong here
Incorrect. The hit counts are 0, so the access-list is not being used.
✗
The UDP connection to 198.51.100.2:53 is being allowed by line 2 of the access-list.
Why it's wrong here
Incorrect. Line 2 has 0 hits, so it is not allowing the traffic.
✓
The access-list 'outside_in' is not applied to any interface or is not the primary access-list governing inbound traffic.
Why this is correct
Correct. The connections exist but the access-list has 0 hits, implying either it is not applied or another rule is allowing traffic (e.g., an implicit permit for established connections).
Related concept
Standard ACLs match source addresses.
✗
The TCP connection to 203.0.113.5:443 is being denied by the implicit deny rule.
Why it's wrong here
Incorrect. The connection exists (flags UIO), so it is not denied.
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 analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. 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. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
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 CISSP ACL questions on filtering logic and placement.
Communication and Network Security — This question tests Communication and Network Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The access-list 'outside_in' is not applied to any interface or is not the primary access-list governing inbound traffic. — The access-list 'outside_in' is applied to the outside interface for inbound traffic. However, the hit counts are all 0, meaning the access-list is not being hit. This suggests that the access-list is not applied to the interface, or the interface has another access-list that allows the traffic, or the connections are established through other means (like stateful inspection). The connections are active, so traffic is passing through the ASA. The access-list with 0 hits indicates it is not the mechanism allowing the traffic.
What should I do if I get this CISSP 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 CISSP ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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