Quick Answer
The answer is a network ACL. This is correct because a network ACL acts as a stateless firewall at the subnet level, allowing you to explicitly define inbound rules that permit SSH traffic (port 22) only from the specific IP range 203.0.113.0/24, while implicitly denying all other traffic. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of the fundamental difference between stateless and stateful filtering: security groups cannot deny traffic by source IP in a single rule (they only allow), making network ACLs the only choice for this kind of IP-based restriction at the subnet boundary. A common trap is confusing security groups with network ACLs, but remember that security groups are stateful and lack explicit deny rules, whereas network ACLs support both allow and deny rules and evaluate them in order. Memory tip: think “ACL = Access Control List = IP-based subnet guard; SG = Security Group = instance-level stateful bouncer.”
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 company wants to ensure that all Amazon EC2 instances in a VPC can only be accessed via SSH from a specific IP address range (203.0.113.0/24). Which VPC component should be used to enforce this restriction?
Security group
Why wrong: Security groups are stateful and only allow rules; they cannot explicitly deny traffic.
Route table
Why wrong: Route tables determine path but do not filter traffic.
Network ACL
Network ACLs are stateless and can deny traffic from IP ranges not in the allowed range.
Internet gateway
Why wrong: An internet gateway provides connectivity but does not filter traffic.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Network ACL
Option A is correct because a network ACL is a stateless firewall that controls inbound and outbound traffic at the subnet level, and can restrict SSH access to a specific IP range. Option B is wrong because security groups are stateful and cannot deny traffic by IP in a single rule (they only allow). Option C is wrong because an internet gateway is not a security control. Option D is wrong because a route table only controls traffic routing, not filtering.
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.
Security group
Why it's wrong here
Security groups are stateful and only allow rules; they cannot explicitly deny traffic.
Route table
Why it's wrong here
Route tables determine path but do not filter traffic.
Network ACL
Why this is correct
Network ACLs are stateless and can deny traffic from IP ranges not in the allowed range.
Related concept
CIDR notation defines the prefix length.
Internet gateway
Why it's wrong here
An internet gateway provides connectivity but does not filter traffic.
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 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
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.
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FAQ
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
The correct answer is: Network ACL — Option A is correct because a network ACL is a stateless firewall that controls inbound and outbound traffic at the subnet level, and can restrict SSH access to a specific IP range. Option B is wrong because security groups are stateful and cannot deny traffic by IP in a single rule (they only allow). Option C is wrong because an internet gateway is not a security control. Option D is wrong because a route table only controls traffic routing, not filtering.
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.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
This SCS-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 SCS-C02 exam.
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