- A
Network Access Control Lists (NACLs)
Why wrong: NACLs are stateless — they evaluate each packet independently. Both inbound and outbound rules must be explicitly created for return traffic. Security groups are stateful and handle return traffic automatically.
- B
AWS WAF rules
Why wrong: WAF inspects HTTP/HTTPS request content for attacks. It does not function as a stateful firewall for general TCP/IP traffic control at the instance level.
- C
Security groups
Security groups are stateful firewalls applied at the instance level. An inbound rule allowing port 443 automatically allows the corresponding return traffic. Only the allowed inbound connections need to be specified.
- D
VPC route tables
Why wrong: Route tables determine where network traffic is directed. They do not filter traffic or provide stateful connection tracking.
Quick Answer
The answer is a security group, which provides the stateful firewall for EC2 instances required to allow inbound HTTPS traffic on port 443 while automatically permitting return traffic. Security groups are stateful by design, meaning that when you create an inbound rule allowing HTTPS, the service tracks the connection state and automatically generates the corresponding outbound return flow without needing an explicit outbound rule. On the AWS Certified Cloud Practitioner CLF-C02 exam, this concept tests your understanding of the fundamental difference between security groups (stateful) and network ACLs (stateless), a common trap where candidates mistakenly choose NACLs because they also filter traffic. Remember the memory tip: "Security groups remember the session; NACLs forget it."
CLF-C02 Security and Compliance Practice Question
This CLF-C02 practice question tests your understanding of security and compliance. 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 needs to allow inbound HTTPS traffic (port 443) to their EC2 web servers while blocking all other inbound traffic. The solution should be stateful — return traffic for allowed inbound connections should automatically be permitted without additional rules. Which AWS feature provides this?
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
Security groups
Security groups act as a stateful virtual firewall for EC2 instances. When you allow inbound HTTPS traffic on port 443, the security group automatically tracks the connection state and permits the corresponding outbound return traffic without requiring an explicit outbound rule. This stateful behavior is inherent to security groups and is the correct choice for the described requirement.
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.
- ✗
Network Access Control Lists (NACLs)
Why it's wrong here
NACLs are stateless — they evaluate each packet independently. Both inbound and outbound rules must be explicitly created for return traffic. Security groups are stateful and handle return traffic automatically.
- ✗
AWS WAF rules
- ✓
Security groups
Why this is correct
Security groups are stateful firewalls applied at the instance level. An inbound rule allowing port 443 automatically allows the corresponding return traffic. Only the allowed inbound connections need to be specified.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
VPC route tables
Why it's wrong here
Route tables determine where network traffic is directed. They do not filter traffic or provide stateful connection tracking.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the stateless nature of Network ACLs with the stateful behavior of security groups, assuming NACLs automatically permit return traffic, which they do not.
Detailed technical explanation
How to think about this question
Security groups implement stateful filtering using connection tracking at the hypervisor layer. When a packet matches an allowed inbound rule, the security group creates a flow entry that tracks the connection's 5-tuple (source IP, destination IP, source port, destination port, protocol). This entry allows all subsequent packets belonging to that connection to pass outbound without an explicit rule, and it automatically expires after the connection ends. In contrast, NACLs require explicit outbound ephemeral port rules (typically 1024-65535) to handle return traffic, which is a common source of 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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Security and Compliance — study guide chapter
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FAQ
Questions learners often ask
What does this CLF-C02 question test?
Security and Compliance — This question tests Security and Compliance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Security groups — Security groups act as a stateful virtual firewall for EC2 instances. When you allow inbound HTTPS traffic on port 443, the security group automatically tracks the connection state and permits the corresponding outbound return traffic without requiring an explicit outbound rule. This stateful behavior is inherent to security groups and is the correct choice for the described requirement.
What should I do if I get this CLF-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.
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Last reviewed: Jun 11, 2026
This CLF-C02 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 CLF-C02 exam.
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