- A
Use network ACLs with inbound rules that reference the prefix list of the previous tier's subnets.
Why wrong: NACLs do not support referencing prefix lists or security groups; they only support CIDR blocks.
- B
Use network ACLs with inbound rules that allow traffic from the previous tier's subnet CIDR.
Why wrong: NACLs are stateless and require separate rules for inbound and outbound traffic, increasing overhead.
- C
Use security groups with inbound rules that allow traffic from the previous tier's public IP addresses.
Why wrong: Using public IPs for internal traffic is not recommended; it's insecure and adds administrative burden.
- D
Use security groups with inbound rules that reference the security group of the previous tier.
Security groups are stateful and can reference other security groups, simplifying rule management.
Multi-Tier Security Group Chaining for Web Applications
This SCS-C02 practice question tests your understanding of infrastructure security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 is designing a network architecture for a multi-tier application. The web tier must be accessible from the internet, while the application tier should only be accessible from the web tier, and the database tier only from the application tier. All tiers are in the same VPC. Which configuration meets these requirements with minimal administrative overhead?
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
Use security groups with inbound rules that reference the security group of the previous tier.
Security groups are stateful and can reference other security groups as a source in inbound rules, allowing traffic from any instance associated with the referenced security group regardless of IP address changes. This creates a logical dependency chain (web SG → app SG → db SG) that enforces the required tier-to-tier access with zero maintenance when instances scale or subnets change. Option D meets the requirement with minimal administrative overhead because security group references automatically adapt to dynamic environments.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use network ACLs with inbound rules that reference the prefix list of the previous tier's subnets.
Why it's wrong here
NACLs do not support referencing prefix lists or security groups; they only support CIDR blocks.
- ✗
Use network ACLs with inbound rules that allow traffic from the previous tier's subnet CIDR.
Why it's wrong here
NACLs are stateless and require separate rules for inbound and outbound traffic, increasing overhead.
- ✗
Use security groups with inbound rules that allow traffic from the previous tier's public IP addresses.
Why it's wrong here
Using public IPs for internal traffic is not recommended; it's insecure and adds administrative burden.
- ✓
Use security groups with inbound rules that reference the security group of the previous tier.
Why this is correct
Security groups are stateful and can reference other security groups, simplifying rule management.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse network ACLs with security groups, assuming stateless ACLs can use logical references like security group IDs, or they overlook the administrative overhead of managing CIDR-based rules in dynamic architectures.
Detailed technical explanation
How to think about this question
Security group references work by evaluating the network interfaces (ENIs) attached to instances in the source security group; AWS automatically resolves the private IPs of those ENIs at the hypervisor level, enabling fine-grained, stateful filtering without manual CIDR management. This mechanism is particularly powerful in auto-scaling environments where instance IPs change frequently, as the security group rule dynamically adapts to the current set of instances. In contrast, network ACLs operate at the subnet level and require explicit rules for ephemeral ports (e.g., 1024-65535) for return traffic, adding complexity and potential for misconfiguration.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use security groups with inbound rules that reference the security group of the previous tier. — Security groups are stateful and can reference other security groups as a source in inbound rules, allowing traffic from any instance associated with the referenced security group regardless of IP address changes. This creates a logical dependency chain (web SG → app SG → db SG) that enforces the required tier-to-tier access with zero maintenance when instances scale or subnets change. Option D meets the requirement with minimal administrative overhead because security group references automatically adapt to dynamic environments.
What should I do if I get this SCS-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 →
Same concept, more angles
2 more ways this is tested on SCS-C02
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 security engineer is designing a network architecture for a three-tier web application. The web tier must be accessible from the internet, the application tier should only be accessible from the web tier, and the database tier should only be accessible from the application tier. Which combination of security groups should be used?
hard- ✓ A.Web: 0.0.0.0/0 on ports 80/443; App: Web SG on port 8080; DB: App SG on port 3306
- B.Web: 0.0.0.0/0 on ports 80/443 and SSH; App: Web SG on port 8080; DB: App SG on port 3306
- C.Web: 0.0.0.0/0 on all ports; App: Web SG on all ports; DB: App SG on all ports
- D.Web: 0.0.0.0/0 on ports 80/443; App: Web SG on ports 8080; DB: App SG on port 3306
Why A: Option A is correct because it properly restricts traffic: the web tier allows only HTTP/HTTPS from the internet (0.0.0.0/0 on ports 80/443), the application tier allows traffic only from the web security group on port 8080, and the database tier allows traffic only from the application security group on port 3306. This enforces the principle of least privilege. Option D is incorrect because it uses 'ports 8080' (plural) instead of 'port 8080' (singular), which is invalid syntax in AWS security group rules.
Variation 2. A security engineer is designing a network architecture for a multi-tier application. The web servers must be accessible from the internet, while the application servers must only be accessible from the web servers. Which TWO configurations should be used? (Choose TWO.)
medium- A.Configure a NAT gateway in the private subnet for the application servers.
- ✓ B.Place the web servers in a public subnet with a route to an internet gateway.
- C.Use a network ACL on the application subnet to allow inbound traffic from the web subnet's IP range.
- D.Place the application servers in a public subnet with a route to an internet gateway.
- ✓ E.Configure the application servers' security group to allow traffic only from the web servers' security group.
Why B: Option B is correct because placing web servers in a public subnet with a route to an internet gateway allows them to receive inbound traffic from the internet. This is the standard AWS design for internet-facing resources, where the subnet's route table directs 0.0.0.0/0 traffic to an internet gateway, enabling direct communication from the internet.
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Last reviewed: Jul 4, 2026
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