Question 685 of 997

Security →easyMultiple ChoiceObjective-mapped

CV0-004 Security Practice Question

This CV0-004 practice question tests your understanding of security. 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 cloud engineer is configuring a web application on AWS and needs to ensure that only HTTP and HTTPS traffic from the internet is allowed to reach the EC2 instances. Which AWS service should be used to control inbound traffic at the instance level?

A
Security Group
Security groups are stateful instance-level firewalls that can allow HTTP/HTTPS inbound traffic.
B
AWS Shield
Why wrong: AWS Shield is a DDoS protection service, not used for basic inbound traffic filtering.
C
AWS WAF
Why wrong: AWS WAF is a web application firewall that protects against web exploits, not a basic traffic control.
D
Network ACL
Why wrong: Network ACLs are stateless and operate at the subnet level, not instance level.

Full breakdown with real-world context →

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 Group

Security groups are stateful virtual firewalls that control inbound and outbound traffic at the instance level. Network ACLs operate at the subnet level and are stateless.

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.

✓
Security Group
Why this is correct
Security groups are stateful instance-level firewalls that can allow HTTP/HTTPS inbound traffic.
Related concept
CIDR notation defines the prefix length.
✗
AWS Shield
Why it's wrong here
AWS Shield is a DDoS protection service, not used for basic inbound traffic filtering.
✗
AWS WAF
Why it's wrong here
AWS WAF is a web application firewall that protects against web exploits, not a basic traffic control.
✗
Network ACL
Why it's wrong here
Network ACLs are stateless and operate at the subnet level, not instance level.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

Visual reference

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 CV0-004 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this CV0-004 question test?

Security — This question tests Security — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Security Group — Security groups are stateful virtual firewalls that control inbound and outbound traffic at the instance level. Network ACLs operate at the subnet level and are stateless.

What should I do if I get this CV0-004 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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Last reviewed: Jul 4, 2026

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