The answer is the first rule blocking all traffic from 10.0.1.0/24, because firewall rules are processed in top-down order and the first match is applied. In this configuration, the initial deny rule explicitly blocks all IP traffic from the 10.0.1.0/24 subnet to any destination, which means any subsequent rules—even a permit for HTTPS on 192.168.1.100—are never evaluated for traffic originating from that subnet. This scenario tests your understanding of implicit versus explicit deny logic and rule precedence, a common pitfall on the CISA exam where candidates mistakenly focus on the HTTPS-specific deny rule or overlook the broader subnet block. The trap is that the second rule appears relevant to the application’s port, but the first rule already catches all traffic from that source. For the exam, remember: “First match wins—a broad deny beats a narrow permit every time.”
CISA Practice Question: Information Systems Operations and Business Resilience
This CISA practice question tests your understanding of information systems operations and business resilience. 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.
Exhibit
access-list extended BLOCK-MALICIOUS
deny ip 10.0.1.0 0.0.0.255 any
deny tcp any host 192.168.1.100 eq 443
permit ip 10.0.0.0 0.0.255.255 any
Refer to the exhibit. During a security audit, an IS analyst identifies that a critical business application hosted on 192.168.1.100:443 is unreachable from the 10.0.1.0/24 subnet. Which of the following is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The first rule blocks all traffic from 10.0.1.0/24
The first rule denies all IP traffic from 10.0.1.0/24 to any destination; this rule takes precedence. The second rule blocks only HTTPS from any source, but the first rule already blocks all traffic from that subnet. The permit rule is for a different subnet.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 first rule blocks all traffic from 10.0.1.0/24
Why this is correct
Correct: The deny rule for the subnet overrides any permit.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The second rule blocks HTTPS traffic from any source to the host
Why it's wrong here
Second rule blocks HTTPS from any source, but first rule already blocks all traffic from 10.0.1.0/24.
✗
The third rule permits all traffic from the 10.0.0.0/16 subnet
Why it's wrong here
The permit rule applies to a larger subnet, but the first rule is more specific and blocks the 10.0.1.0/24 range.
✗
The firewall is misconfigured for TCP traffic
Why it's wrong here
Configuration is explicit; no general misconfiguration.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CISA subnetting questions on CIDR, address ranges, and subnet selection.
Information Systems Operations and Business Resilience — This question tests Information Systems Operations and Business Resilience — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The first rule blocks all traffic from 10.0.1.0/24 — The first rule denies all IP traffic from 10.0.1.0/24 to any destination; this rule takes precedence. The second rule blocks only HTTPS from any source, but the first rule already blocks all traffic from that subnet. The permit rule is for a different subnet.
What should I do if I get this CISA question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CISA subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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