Quick Answer
The answer is to use managed prefix lists in security group rules, as this allows you to reference a collection of CIDR blocks by a single logical name rather than maintaining dozens of individual inbound rules. By creating a prefix list that aggregates the CIDR ranges of all connected VPCs, you can simplify security group management dramatically—any update to the prefix list automatically propagates to every security group referencing it, preserving the same level of granularity without manual rule edits. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of how prefix lists reduce operational overhead in multi-VPC transit gateway architectures, a common scenario where security groups would otherwise become unwieldy. A frequent trap is confusing prefix lists with NACLs or Network Firewall, but remember that prefix lists are purpose-built for simplifying security group rules, not for stateless filtering or deep packet inspection. Memory tip: think of a prefix list as a “CIDR shortcut” for your security groups—one name, many ranges, zero complexity.
This ANS-C01 practice question tests your understanding of network implementation. 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.
A company has multiple VPCs connected via a transit gateway. Each VPC has a security group that allows traffic from the other VPCs' CIDR blocks. The security group rules are getting complex. How can the company simplify security group management while maintaining the same level of security?
Use managed prefix lists in security group rules.
Prefix lists simplify by grouping CIDRs.
Use VPC endpoints for inter-VPC communication.
Why wrong: VPC endpoints are for AWS services, not VPCs.
Deploy AWS Network Firewall to centralize rules.
Why wrong: Adds another layer, not simplification.
Replace security groups with network ACLs.
Why wrong: NACLs are stateless and do not simplify.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use managed prefix lists in security group rules.
Option D is correct because using prefix lists allows referencing a CIDR collection in security group rules. Option A is wrong because NACLs are stateless and less granular. Option B is wrong because VPC endpoints are for AWS services. Option C is wrong because Network Firewall adds complexity.
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
For each option: why learners choose it and why it is or isn't the right answer here.
Use managed prefix lists in security group rules.
Why this is correct
Prefix lists simplify by grouping CIDRs.
Related concept
CIDR notation defines the prefix length.
Use VPC endpoints for inter-VPC communication.
Why it's wrong here
VPC endpoints are for AWS services, not VPCs.
Deploy AWS Network Firewall to centralize rules.
Why it's wrong here
Adds another layer, not simplification.
Replace security groups with network ACLs.
Why it's wrong here
NACLs are stateless and do not simplify.
Common exam traps
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
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.
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
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
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
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
The correct answer is: Use managed prefix lists in security group rules. — Option D is correct because using prefix lists allows referencing a CIDR collection in security group rules. Option A is wrong because NACLs are stateless and less granular. Option B is wrong because VPC endpoints are for AWS services. Option C is wrong because Network Firewall adds complexity.
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.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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.
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