← ANS-C01·Amazon Web Services

Question 985 of 1,705

Network Security, Compliance and Governance →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to 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. This is correct because security groups act as a stateful, instance-level firewall, allowing granular port control for cross-account VPC peering traffic, whereas network ACLs are stateless and operate at the subnet level without supporting security group references. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding that cross-account VPC peering does not support direct security group referencing by default—you must explicitly specify the peered VPC’s CIDR or security group ID in the inbound rules. A common trap is assuming network ACLs can enforce port restrictions at the instance level, but they lack stateful inspection and cannot reference security groups. Memory tip: “SG for port control at the instance; NACL for subnet-level stateless rules.”

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?

Question 1hardmultiple choice

Review the full routing breakdown →

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 B is correct because security groups can be used to control traffic at the instance level based on ports. Option A is wrong because VPC peering does not support security group referencing across accounts by default; you need to update the security group to reference the peered VPC's security group. Option C is wrong because network ACLs are stateless and apply at the subnet level, not at the instance level, and they cannot reference security groups. Option D is wrong because network ACLs do not support stateful inspection like security groups.

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.

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.

Related ANS-C01 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Network Management and Operations practice questions

Practise ANS-C01 questions linked to Network Management and Operations.

Network Security, Compliance and Governance practice questions

Practise ANS-C01 questions linked to Network Security, Compliance and Governance.

Network Design practice questions

Practise ANS-C01 questions linked to Network Design.

Network Implementation practice questions

Practise ANS-C01 questions linked to Network Implementation.

ANS-C01 fundamentals practice questions

Practise ANS-C01 questions linked to ANS-C01 fundamentals.

ANS-C01 scenario practice questions

Practise ANS-C01 questions linked to ANS-C01 scenario.

ANS-C01 troubleshooting practice questions

Practise ANS-C01 questions linked to ANS-C01 troubleshooting.

Practice this exam

Start a free ANS-C01 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

ANS-C01 practice-test guide →Study guide →Browse all practice tests

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 B is correct because security groups can be used to control traffic at the instance level based on ports. Option A is wrong because VPC peering does not support security group referencing across accounts by default; you need to update the security group to reference the peered VPC's security group. Option C is wrong because network ACLs are stateless and apply at the subnet level, not at the instance level, and they cannot reference security groups. Option D is wrong because network ACLs do not support stateful inspection like security groups.

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.

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 →

How Courseiva writes practice questions · Editorial policy

Last reviewed: Jun 20, 2026

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.

Loading comments…

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.