The correct answer is that the connection is dropped by iptables. This happens because iptables operates as a host-based firewall on the EC2 instance itself, processing packets after the security group has already allowed them. While the security group permits HTTP from 0.0.0.0/0, the iptables INPUT chain has a default DROP policy and only allows HTTP from the 10.0.0.0/16 subnet, so the packet from 203.0.113.5 is dropped. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding that security groups act as a virtual firewall at the VPC level, while iptables controls traffic at the OS level, and iptables rules can override security group permissions. A common trap is assuming a security group allow means the instance will accept the traffic, but iptables can still block it. Remember the memory tip: security groups are the bouncer at the club door, but iptables is the security guard inside who can still turn you away.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure 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.
Network Topology
Refer to the exhibit. A security engineer runs the iptables command on an EC2 instance in a VPC. The instance has a security group that allows all outbound traffic and inbound SSH from 0.0.0.0/0, HTTP from 0.0.0.0/0, and HTTPS from 0.0.0.0/0. A user from IP 203.0.113.5 tries to connect to the instance over HTTP. What will happen?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The connection is dropped by iptables.
Option B is correct because the iptables INPUT chain has a default DROP policy. The rules only allow HTTP (port 80) from the 10.0.0.0/16 subnet, but the user's IP is 203.0.113.5, which is not in that range. Therefore, the packet is dropped by iptables. Option A is wrong because even though the security group allows HTTP, iptables drops it. Option C is wrong because SSH is allowed only from anywhere, but the request is HTTP. Option D is wrong because the security group allows HTTP, but iptables overrides.
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.
✗
The connection succeeds because the security group allows HTTP.
Why it's wrong here
Security groups are stateful but iptables can override.
✗
The connection succeeds because iptables allows HTTP from anywhere.
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The connection is dropped by iptables. — Option B is correct because the iptables INPUT chain has a default DROP policy. The rules only allow HTTP (port 80) from the 10.0.0.0/16 subnet, but the user's IP is 203.0.113.5, which is not in that range. Therefore, the packet is dropped by iptables. Option A is wrong because even though the security group allows HTTP, iptables drops it. Option C is wrong because SSH is allowed only from anywhere, but the request is HTTP. Option D is wrong because the security group allows HTTP, but iptables overrides.
What should I do if I get this SCS-C02 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 SCS-C02 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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