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PAS-C01 Migration Practice Question

This PAS-C01 practice question tests your understanding of migration. 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.

Network Topology

Refer to the exhibit. An EC2 instance is running and has a public IP address. A security engineer needs to verify that the instance is not publicly accessible from the internet. Which additional step is required?

Network Topology

A
Check if the instance has a public IP.
Why wrong: Option A is incorrect because having a public IP does not guarantee internet accessibility; additional checks on inbound traffic controls are required to confirm the instance is not publicly accessible.
B
Check the route table for an internet gateway.
Why wrong: Checking the route table for an internet gateway is necessary for outbound traffic or inbound traffic that is initiated externally, but it does not determine whether inbound traffic to the instance is allowed. The security group must also permit the traffic.
C
Check the security group inbound rules.
The security group inbound rules explicitly control which traffic is allowed to reach the instance. To verify that the instance is not publicly accessible, you must check that no inbound rules allow traffic from 0.0.0.0/0 or any other public source.
D
Check the network ACL of the subnet.
Why wrong: Network ACLs provide stateless filtering at the subnet level, but they are not the primary control for instance-level inbound traffic. Even if the NACL allows traffic, the security group must also allow it; therefore, checking the security group is the additional step required.

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

✓

Check the security group inbound rules.

Option C is correct because security group inbound rules determine whether traffic from the internet is allowed to reach the instance. Option A is incorrect because having a public IP does not guarantee accessibility; the security group must allow inbound traffic. Option B is incorrect because the route table's internet gateway entry is necessary but not sufficient; inbound rules must permit access. Option D is incorrect because network ACLs provide stateless filtering at the subnet level, but the question specifically requires verifying that the instance is not publicly accessible, which is primarily controlled by security group inbound rules.

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.

✗
Check if the instance has a public IP.
Why it's wrong here
Option A is incorrect because having a public IP does not guarantee internet accessibility; additional checks on inbound traffic controls are required to confirm the instance is not publicly accessible.
✗
Check the route table for an internet gateway.
Why it's wrong here
Checking the route table for an internet gateway is necessary for outbound traffic or inbound traffic that is initiated externally, but it does not determine whether inbound traffic to the instance is allowed. The security group must also permit the traffic.
✓
Check the security group inbound rules.
Why this is correct
The security group inbound rules explicitly control which traffic is allowed to reach the instance. To verify that the instance is not publicly accessible, you must check that no inbound rules allow traffic from 0.0.0.0/0 or any other public source.
Related concept
CIDR notation defines the prefix length.
✗
Check the network ACL of the subnet.
Why it's wrong here
Network ACLs provide stateless filtering at the subnet level, but they are not the primary control for instance-level inbound traffic. Even if the NACL allows traffic, the security group must also allow it; therefore, checking the security group is the additional step required.

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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this PAS-C01 question test?

Migration — This question tests Migration — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Check the security group inbound rules. — Option C is correct because security group inbound rules determine whether traffic from the internet is allowed to reach the instance. Option A is incorrect because having a public IP does not guarantee accessibility; the security group must allow inbound traffic. Option B is incorrect because the route table's internet gateway entry is necessary but not sufficient; inbound rules must permit access. Option D is incorrect because network ACLs provide stateless filtering at the subnet level, but the question specifically requires verifying that the instance is not publicly accessible, which is primarily controlled by security group inbound rules.

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

What is the key concept behind this question?

CIDR notation defines the prefix length.

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