Quick Answer
The correct choice is Transit Gateway with a security appliance in a central VPC. This architecture enables centralized traffic inspection by routing all inter-subnet traffic through a middlebox appliance, such as a firewall, deployed in a shared services VPC, allowing you to enforce security policies without point-to-point peering. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how Transit Gateway acts as a hub for transitive routing and central inspection, often appearing as a trap where VPC peering (point-to-point, not centralized) or AWS Network Firewall (a service, not the architectural glue) are distractors. Remember the key distinction: Transit Gateway provides the network fabric for central inspection, while the security appliance does the actual filtering. Memory tip: think “hub-and-spoke with a firewall in the hub” to instantly recall the correct design.
This ANS-C01 practice question tests your understanding of network management and operations. 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 a VPC with multiple subnets. They want to centrally manage and inspect all traffic between subnets using a security appliance. Which AWS service should be used to achieve this?
VPC peering
Why wrong: Not centralized.
AWS Route 53 Resolver
Why wrong: DNS only.
AWS Network Firewall
Why wrong: Can inspect traffic but Transit Gateway is the connectivity hub.
Transit Gateway with a security appliance in a central VPC
Allows centralized inspection.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Transit Gateway with a security appliance in a central VPC
Option B is correct because Transit Gateway with a middlebox appliance (e.g., firewall) in a shared services VPC allows traffic inspection. Option A is wrong because VPC peering is point-to-point and not centralized. Option C is wrong because AWS Network Firewall can be used but Transit Gateway provides the architecture for central inspection. Option D is wrong because Route 53 is DNS.
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.
VPC peering
Why it's wrong here
Not centralized.
AWS Route 53 Resolver
Why it's wrong here
DNS only.
AWS Network Firewall
Why it's wrong here
Can inspect traffic but Transit Gateway is the connectivity hub.
Transit Gateway with a security appliance in a central VPC
Why this is correct
Allows centralized inspection.
Related concept
CIDR notation defines the prefix length.
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 Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..
The correct answer is: Transit Gateway with a security appliance in a central VPC — Option B is correct because Transit Gateway with a middlebox appliance (e.g., firewall) in a shared services VPC allows traffic inspection. Option A is wrong because VPC peering is point-to-point and not centralized. Option C is wrong because AWS Network Firewall can be used but Transit Gateway provides the architecture for central inspection. Option D is wrong because Route 53 is DNS.
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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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses a centralized inspection VPC for traffic inspection. All VPCs route traffic to the inspection VPC via Transit Gateway. The security team wants to ensure that all traffic between VPCs is inspected by a network virtual appliance in the inspection VPC. Which Transit Gateway feature should be configured?
mediumWhy A: Option D is correct because Transit Gateway flow logs can be used to verify that traffic is flowing as expected. Option A is wrong because Transit Gateway peering is for connecting TGWs, not for inspection. Option B is wrong because Transit Gateway route tables are used for routing decisions, not for ensuring inspection. Option C is wrong because Transit Gateway multicast is for multicast traffic.
Last reviewed: Jun 20, 2026
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