The correct answer is that SSH access is limited to the 10.0.0.0/8 subnet. This is because the ACL inbound rule explicitly permits TCP port 22 only from source IP addresses within the 10.0.0.0/8 range, and the implicit deny at the end of the ACL blocks all other traffic, including SSH from any other subnet. On the Certified Information Systems Security Professional CISSP exam, this concept tests your understanding of how access control lists enforce network segmentation and the principle of least privilege, often appearing in questions about securing administrative access. A common trap is forgetting that an implicit deny exists at the end of every ACL, so without an explicit permit for SSH from other subnets, all other sources are blocked. Memory tip: “Permit first, deny last—if it’s not listed, it’s blasted.”
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SSH access is limited to the 10.0.0.0/8 subnet.
Option A is correct because the ACL inbound rule explicitly permits TCP port 22 (SSH) only from source IP addresses within the 10.0.0.0/8 range, and the implicit deny at the end of the ACL blocks all other traffic, including SSH from any other subnet. This restricts SSH administrative access to the private 10.0.0.0/8 network, enhancing security by preventing external SSH connections.
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.
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the implicit deny at the end of an ACL, leading candidates to overlook that even though a rule permits HTTP, the absence of a specific deny for HTTP does not mean it is denied—only the implicit deny blocks unmatched traffic, but here HTTP is explicitly permitted.
Trap categories for this question
Command / output trap
This is true but not the most relevant; the exhibit shows inbound rules only.
Detailed technical explanation
How to think about this question
In Cisco IOS, ACLs apply an implicit 'deny any' at the end, meaning any traffic not explicitly permitted is dropped. The order of entries matters because ACLs are processed top-down; once a match is found, no further rules are evaluated. In real-world scenarios, misordering ACL entries can inadvertently block desired traffic or allow unwanted traffic, making rule sequence a critical design consideration.
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: SSH access is limited to the 10.0.0.0/8 subnet. — Option A is correct because the ACL inbound rule explicitly permits TCP port 22 (SSH) only from source IP addresses within the 10.0.0.0/8 range, and the implicit deny at the end of the ACL blocks all other traffic, including SSH from any other subnet. This restricts SSH administrative access to the private 10.0.0.0/8 network, enhancing security by preventing external SSH connections.
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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