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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 troubleshooting connectivity issues between two VPCs connected via a VPC Peering connection. The VPCs are in different accounts. The security groups in both VPCs allow traffic between the CIDRs. The route tables have the appropriate entries. However, instances in VPC A cannot communicate with instances in VPC B. 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.

A
The VPC Peering connection does not support transitive routing through an intermediate VPC or on-premises network.
VPC Peering is non-transitive; if there is a VPN or another VPC in the path, traffic will be dropped.
B
The VPC Peering connection requires an IAM role to be assumed for cross-account communication.
Why wrong: VPC Peering can work cross-account without IAM roles; only the route tables and security groups need configuration.
C
The security group in VPC A does not allow inbound traffic from VPC B's CIDR.
Why wrong: Security groups are stateful; if outbound is allowed, return traffic is automatically allowed.
D
The network ACL in VPC A does not allow return traffic from VPC B.
Why wrong: NACLs are stateless and must allow both inbound and outbound traffic; but the issue is likely not NACLs if security groups are configured.

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

✓

The VPC Peering connection does not support transitive routing through an intermediate VPC or on-premises network.

Option A is correct because VPC Peering connections do not support transitive routing. If traffic must pass through an intermediate VPC or on-premises network, the peering connection alone cannot route it. Option B is incorrect because VPC Peering does not require an IAM role for cross-account communication; instead, the accepter must accept the request and route tables must be updated. Option C is incorrect because security groups are stateful and automatically allow return traffic, and the scenario states security groups allow traffic between CIDRs. Option D is incorrect because the issue is not about NACLs; if NACLs were blocking traffic, the problem would likely be related to stateless filtering, but the question focuses on security groups and routing.

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 VPC Peering connection does not support transitive routing through an intermediate VPC or on-premises network.
Why this is correct
VPC Peering is non-transitive; if there is a VPN or another VPC in the path, traffic will be dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The VPC Peering connection requires an IAM role to be assumed for cross-account communication.
Why it's wrong here
VPC Peering can work cross-account without IAM roles; only the route tables and security groups need configuration.
✗
The security group in VPC A does not allow inbound traffic from VPC B's CIDR.
Why it's wrong here
Security groups are stateful; if outbound is allowed, return traffic is automatically allowed.
✗
The network ACL in VPC A does not allow return traffic from VPC B.
Why it's wrong here
NACLs are stateless and must allow both inbound and outbound traffic; but the issue is likely not NACLs if security groups are configured.

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: The VPC Peering connection does not support transitive routing through an intermediate VPC or on-premises network. — Option A is correct because VPC Peering connections do not support transitive routing. If traffic must pass through an intermediate VPC or on-premises network, the peering connection alone cannot route it. Option B is incorrect because VPC Peering does not require an IAM role for cross-account communication; instead, the accepter must accept the request and route tables must be updated. Option C is incorrect because security groups are stateful and automatically allow return traffic, and the scenario states security groups allow traffic between CIDRs. Option D is incorrect because the issue is not about NACLs; if NACLs were blocking traffic, the problem would likely be related to stateless filtering, but the question focuses on security groups and routing.

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

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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