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
access-list outside_in extended permit tcp any host 192.168.1.10 eq 443
access-list outside_in extended permit tcp any host 192.168.1.10 eq 80
access-list outside_in extended deny ip any any
Refer to the exhibit. The firewall rules above are applied to the outside interface. A penetration tester from the internet attempts to establish a connection to 192.168.1.10 on TCP port 8080. What will happen?
access-list outside_in extended permit tcp any host 192.168.1.10 eq 443
access-list outside_in extended permit tcp any host 192.168.1.10 eq 80
access-list outside_in extended deny ip any any
A
The connection is permitted only if the tester uses a VPN
Why wrong: VPN access would change the source IP, but the ACL would still filter on destination port; unless VPN traffic is processed differently, the port restriction remains.
B
The connection is permitted
Why wrong: Port 8080 is not listed in the permit rules, so the connection is not permitted.
C
The connection is denied because the destination is not reachable
Why wrong: The destination is reachable; the denial is due to the ACL, not routing.
D
The connection is denied because the port is not explicitly allowed
The firewall denies any traffic not matching a permit rule due to the implicit deny.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The connection is denied because the port is not explicitly allowed
Option D is correct because firewall rules operate on an implicit-deny model: if no rule explicitly permits traffic, it is denied by default. Since the exhibit shows no rule allowing TCP port 8080 from the internet to 192.168.1.10, the connection is dropped. The destination is reachable (192.168.1.10 is a valid internal IP), but the lack of an explicit permit for port 8080 causes the denial.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 connection is permitted only if the tester uses a VPN
Why it's wrong here
VPN access would change the source IP, but the ACL would still filter on destination port; unless VPN traffic is processed differently, the port restriction remains.
✗
The connection is permitted
Why it's wrong here
Port 8080 is not listed in the permit rules, so the connection is not permitted.
✗
The connection is denied because the destination is not reachable
Why it's wrong here
The destination is reachable; the denial is due to the ACL, not routing.
✓
The connection is denied because the port is not explicitly allowed
Why this is correct
The firewall denies any traffic not matching a permit rule due to the implicit deny.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a destination IP is reachable if it exists on the network, but the question tests the understanding that firewall rules control access based on port and protocol, not just IP reachability.
Detailed technical explanation
How to think about this question
Firewalls process rules sequentially from top to bottom, applying the first match; if no match is found, the implicit deny (often a 'deny ip any any' at the end) drops the packet. In Cisco ACLs, this implicit deny is not shown in the rule list but is always present. A common real-world scenario is misconfiguring web proxies or reverse proxies where port 8080 is used internally but forgotten in the ACL, leading to silent failures that are hard to troubleshoot without packet captures.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. 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.
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The connection is denied because the port is not explicitly allowed — Option D is correct because firewall rules operate on an implicit-deny model: if no rule explicitly permits traffic, it is denied by default. Since the exhibit shows no rule allowing TCP port 8080 from the internet to 192.168.1.10, the connection is dropped. The destination is reachable (192.168.1.10 is a valid internal IP), but the lack of an explicit permit for port 8080 causes the denial.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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