The answer is to deploy an AWS Network Firewall in the VPC and configure domain filtering rules. This is the most secure way to restrict outbound traffic to specific domains because AWS Network Firewall performs stateful, application-layer inspection, allowing you to filter HTTPS traffic by domain name (e.g., api.example.com) rather than just IP addresses, which can change. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of the limitations of security groups and NACLs—security groups cannot filter by domain name, and NACLs are stateless and lack application awareness. A common trap is assuming a VPC endpoint for S3 or a simple egress-only rule will suffice, but neither provides domain-level control for general HTTPS traffic. Memory tip: think “Firewall for FQDNs”—when you need to allow traffic to specific domain names, reach for a stateful firewall, not a stateless filter.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 needs to restrict outbound traffic from a VPC to only allow HTTPS traffic to specific domains (e.g., api.example.com). The VPC has a NAT gateway in a public subnet. What is the most secure way to implement this restriction?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy an AWS Network Firewall in the VPC and configure domain filtering rules.
Option D is correct. Using an AWS Network Firewall or a third-party firewall appliance allows stateful inspection of traffic and can filter by domain name. Option A (security group egress rules) cannot filter by domain name. Option B (NACL) is stateless and cannot inspect domain names. Option C (VPC endpoint for S3) is for S3, not general HTTPS.
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.
✗
Configure security group egress rules to allow HTTPS to 0.0.0.0/0.
Why it's wrong here
This allows all HTTPS traffic, not restricted to specific domains.
✓
Deploy an AWS Network Firewall in the VPC and configure domain filtering rules.
Why this is correct
Network Firewall can filter outbound traffic by domain name with TLS inspection.
Configure network ACL outbound rules to allow HTTPS to the IP addresses of the allowed domains.
Why it's wrong here
IP addresses can change; NACL is stateless and harder to manage.
✗
Create a VPC endpoint for Amazon S3 and route traffic through it.
Why it's wrong here
VPC endpoints are for AWS services, not filtering traffic to arbitrary domains.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Deploy an AWS Network Firewall in the VPC and configure domain filtering rules. — Option D is correct. Using an AWS Network Firewall or a third-party firewall appliance allows stateful inspection of traffic and can filter by domain name. Option A (security group egress rules) cannot filter by domain name. Option B (NACL) is stateless and cannot inspect domain names. Option C (VPC endpoint for S3) is for S3, not general HTTPS.
What should I do if I get this SCS-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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