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Question 985 of 1,705

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 company is setting up a cross-account VPC peering connection between VPC A (account 1) and VPC B (account 2). The security team wants to ensure that only specific TCP ports are allowed between the VPCs. They have configured the route tables and the VPC peering connection is active. Which additional configuration is required to enforce the port restriction?

A
Modify the network ACLs in both VPCs to allow inbound traffic only on the required ports.
Why wrong: Network ACLs apply to subnets, not instances, and cannot reference security groups.
B
Use network ACLs with stateful filtering to allow only the required ports.
Why wrong: Network ACLs are stateless and require rules for both inbound and outbound traffic; they do not provide stateful filtering.
C
Update the security groups in both VPCs to allow inbound traffic only on the required ports from the peered VPC's CIDR or security group.
Security groups can restrict traffic based on port and protocol at the instance level.
D
Configure the route tables to deny traffic on all ports except the allowed ones.
Why wrong: Route tables only control traffic direction, not port filtering.

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

✓

Update the security groups in both VPCs to allow inbound traffic only on the required ports from the peered VPC's CIDR or security group.

Option C is correct because security groups can reference security groups from peered VPCs across accounts when the VPC peering connection is active, allowing fine-grained control over specific TCP ports at the instance level. Option A is incorrect because modifying network ACLs is possible but they are stateless and apply at the subnet level, not instance level; also, network ACLs cannot reference security groups from peered VPCs. Option B is incorrect because network ACLs are stateless, not stateful; security groups are stateful. Option D is incorrect because route tables control the path of traffic, not port-level filtering; they cannot deny traffic based on ports.

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.

✗
Modify the network ACLs in both VPCs to allow inbound traffic only on the required ports.
Why it's wrong here
Network ACLs apply to subnets, not instances, and cannot reference security groups.
✗
Use network ACLs with stateful filtering to allow only the required ports.
Why it's wrong here
Network ACLs are stateless and require rules for both inbound and outbound traffic; they do not provide stateful filtering.
✓
Update the security groups in both VPCs to allow inbound traffic only on the required ports from the peered VPC's CIDR or security group.
Why this is correct
Security groups can restrict traffic based on port and protocol at the instance level.
Related concept
CIDR notation defines the prefix length.
✗
Configure the route tables to deny traffic on all ports except the allowed ones.
Why it's wrong here
Route tables only control traffic direction, not port filtering.

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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

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: Update the security groups in both VPCs to allow inbound traffic only on the required ports from the peered VPC's CIDR or security group. — Option C is correct because security groups can reference security groups from peered VPCs across accounts when the VPC peering connection is active, allowing fine-grained control over specific TCP ports at the instance level. Option A is incorrect because modifying network ACLs is possible but they are stateless and apply at the subnet level, not instance level; also, network ACLs cannot reference security groups from peered VPCs. Option B is incorrect because network ACLs are stateless, not stateful; security groups are stateful. Option D is incorrect because route tables control the path of traffic, not port-level filtering; they cannot deny traffic based on ports.

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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