The correct answer is an outbound rule with Type: HTTPS, Protocol: TCP, Port: 443, and Destination: 203.0.113.0/24. This is because security group outbound rules always specify a destination CIDR block, not a source, which is reserved for inbound rules. When designing a security group outbound rule for HTTPS to a specific IP range, you must explicitly define the target network using CIDR notation, as security groups do not support prefix lists for destinations and cannot use a /32 when the requirement is a /24 range. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of stateful filtering and the directional nature of security group rules—a common trap is confusing source and destination fields or assuming prefix lists apply to outbound destinations. Remember the memory tip: "Outbound goes to a destination CIDR, inbound comes from a source CIDR"—keep the direction straight to avoid the trap.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 is designing a security group rule to allow outbound HTTPS traffic (TCP 443) to a specific external service IP range 203.0.113.0/24. The security group is attached to a fleet of EC2 instances. Which rule should be added?
Option D is correct because security group outbound rules require a destination CIDR. Option A is wrong because source is for inbound rules. Option B is wrong because security groups do not use prefix lists for destinations. Option C is wrong because the IP range is /24, not /32.
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.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Type: HTTPS, Protocol: TCP, Port: 443, Destination: 203.0.113.0/24 — Option D is correct because security group outbound rules require a destination CIDR. Option A is wrong because source is for inbound rules. Option B is wrong because security groups do not use prefix lists for destinations. Option C is wrong because the IP range is /24, not /32.
What should I do if I get this ANS-C01 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 ANS-C01 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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