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Network Security, Compliance and Governance →hardMultiple ChoiceObjective-mapped

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.

A security engineer is configuring Network Access Control Lists (NACLs) for a VPC with multiple subnets. The engineer wants to block SSH access (port 22) from a specific IP range 10.0.0.0/8 to the entire VPC CIDR (172.16.0.0/16). What is the most effective approach?

A
Add inbound and outbound NACL rules denying SSH from 10.0.0.0/8
Correct. NACLs are stateless, so to block SSH traffic from 10.0.0.0/8 to the VPC CIDR, you must add both an inbound rule denying SSH from that source and an outbound rule denying SSH to that source as return traffic will be seen as a new flow.
B
Add a security group rule to deny inbound SSH from 10.0.0.0/8
Why wrong: Incorrect. Security groups are stateful and cannot be used to deny traffic; they only support allow rules. Also, a security group rule cannot explicitly deny traffic from a specific IP range.
C
Add an inbound NACL rule denying SSH from 10.0.0.0/8
Why wrong: Incorrect. Adding only an inbound NACL rule denies incoming SSH but does not block the return traffic (outbound). Since NACLs are stateless, both directions must be explicitly denied.
D
Add an outbound security group rule denying SSH to 10.0.0.0/8
Why wrong: Incorrect. Security groups are stateful and work at the instance level. They cannot block traffic based on destination IP in an outbound rule easily, and they only allow, not deny.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Add inbound and outbound NACL rules denying SSH from 10.0.0.0/8

NACLs are stateless, so to block SSH from 10.0.0.0/8 to the entire VPC, both inbound and outbound rules are needed. Option A correctly adds both rules. Option B is incorrect because security groups are stateful and only allow traffic; they cannot deny. Option C is incorrect because an inbound rule alone does not block return traffic. Option D is incorrect because security groups cannot block outbound traffic based on destination IP effectively.

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.

✓
Add inbound and outbound NACL rules denying SSH from 10.0.0.0/8
Why this is correct
Correct. NACLs are stateless, so to block SSH traffic from 10.0.0.0/8 to the VPC CIDR, you must add both an inbound rule denying SSH from that source and an outbound rule denying SSH to that source as return traffic will be seen as a new flow.
Related concept
CIDR notation defines the prefix length.
✗
Add a security group rule to deny inbound SSH from 10.0.0.0/8
Why it's wrong here
Incorrect. Security groups are stateful and cannot be used to deny traffic; they only support allow rules. Also, a security group rule cannot explicitly deny traffic from a specific IP range.
✗
Add an inbound NACL rule denying SSH from 10.0.0.0/8
Why it's wrong here
Incorrect. Adding only an inbound NACL rule denies incoming SSH but does not block the return traffic (outbound). Since NACLs are stateless, both directions must be explicitly denied.
✗
Add an outbound security group rule denying SSH to 10.0.0.0/8
Why it's wrong here
Incorrect. Security groups are stateful and work at the instance level. They cannot block traffic based on destination IP in an outbound rule easily, and they only allow, not deny.

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.

Visual reference

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.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

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: Add inbound and outbound NACL rules denying SSH from 10.0.0.0/8 — NACLs are stateless, so to block SSH from 10.0.0.0/8 to the entire VPC, both inbound and outbound rules are needed. Option A correctly adds both rules. Option B is incorrect because security groups are stateful and only allow traffic; they cannot deny. Option C is incorrect because an inbound rule alone does not block return traffic. Option D is incorrect because security groups cannot block outbound traffic based on destination IP effectively.

What should I do if I get this ANS-C01 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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