The answer is the inbound deny rule for TCP (port range) blocks all TCP traffic. This is correct because network ACL rule evaluation order follows ascending rule numbers, so Rule 100, which denies all TCP traffic from 0.0.0.0/0, is evaluated before Rule 200’s allow-all rule, causing the HTTP traffic to be denied regardless of the later permit. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of stateless packet filtering and the critical difference between security groups (which evaluate all rules before deciding) and network ACLs (which stop at the first matching rule). A common trap is assuming a later allow rule overrides an earlier deny, but in network ACLs, order is absolute. Remember the mnemonic: “First match wins, so deny before allow kills the flow.”
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Network Topology
Refer to the exhibit. A network engineer runs the above command and sees this network ACL configuration. The subnet associated with this ACL contains an EC2 instance that is failing to receive inbound HTTP traffic (TCP 80) from the internet. What 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 inbound deny rule for TCP (port range) blocks all TCP traffic
Option A is correct. The inbound deny rule (Rule 100) for TCP (Protocol 6) from 0.0.0.0/0 denies all TCP traffic, including HTTP. Even though there is a later allow-all rule (Rule 200), network ACLs evaluate rules in ascending order, so the deny rule is evaluated first and blocks the traffic. Option B is wrong because the outbound rule allows all traffic. Option C is wrong because the allow rule exists but is after the deny. Option D is wrong because the deny rule applies to all CIDR blocks.
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 inbound deny rule is associated with the wrong subnet
Why it's wrong here
The ACL is associated with the subnet, and the deny rule applies to all traffic from 0.0.0.0/0.
✓
The inbound deny rule for TCP (port range) blocks all TCP traffic
Why this is correct
Rule number 100 denies TCP traffic (protocol 6) from 0.0.0.0/0, which includes HTTP (TCP 80). The rule is evaluated before the allow rule.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The outbound rule allows all traffic (protocol -1), so return traffic is allowed.
✗
The inbound allow rule is not wide enough
Why it's wrong here
The allow rule (Rule 200) allows all traffic, but it is never reached because the deny rule is evaluated first.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The inbound deny rule for TCP (port range) blocks all TCP traffic — Option A is correct. The inbound deny rule (Rule 100) for TCP (Protocol 6) from 0.0.0.0/0 denies all TCP traffic, including HTTP. Even though there is a later allow-all rule (Rule 200), network ACLs evaluate rules in ascending order, so the deny rule is evaluated first and blocks the traffic. Option B is wrong because the outbound rule allows all traffic. Option C is wrong because the allow rule exists but is after the deny. Option D is wrong because the deny rule applies to all CIDR blocks.
What should I do if I get this ANS-C01 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 ANS-C01 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.