The correct answer is to remove the default route (0.0.0.0/0) pointing to an internet gateway or NAT gateway from the private subnet’s route table. This works because outbound internet access from a private subnet is governed entirely by its route table; without a route directing traffic to an internet gateway or NAT device, any packet destined for the internet has no path and is dropped, effectively blocking outbound connectivity. On the AWS Certified Security Specialty SCS-C02 exam, this concept tests your understanding of how subnet routing controls network boundaries, and it often appears as a distractor where candidates mistakenly apply security group or network ACL rules instead. A common trap is assuming security groups can block outbound traffic initiated from within the subnet, but they are stateful and allow return traffic automatically. Remember the memory tip: “No route, no outbound”—if the route table lacks a 0.0.0.0/0 target, the subnet is isolated from the internet regardless of other firewall rules.
SCS-C02 Infrastructure Security Practice Question
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 has deployed a multi-tier web application on AWS. The web servers are in a public subnet, and the application servers are in a private subnet. The security team wants to ensure that the application servers cannot initiate outbound connections to the internet. What should the team do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the default route (0.0.0.0/0) pointing to an internet gateway or NAT gateway from the private subnet's route table.
Option C is correct because a route table with only a local route and no internet gateway or NAT gateway prevents outbound internet traffic. Option A is wrong because security groups are stateful and allowing inbound traffic may inadvertently allow outbound responses. Option B is wrong because network ACLs are stateless and need explicit deny rules, but a route-based approach is simpler. Option D is wrong because an egress-only internet gateway is for IPv6, not IPv4.
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.
✗
Add a deny rule for all outbound traffic in the network ACL of the private subnet.
Why it's wrong here
Network ACLs are stateless and require explicit allow rules for responses; this could break traffic.
✗
Modify the security group of the application servers to deny all outbound traffic.
Why it's wrong here
Security groups are stateful; if inbound is allowed, outbound responses are allowed automatically.
✓
Remove the default route (0.0.0.0/0) pointing to an internet gateway or NAT gateway from the private subnet's route table.
Why this is correct
Without a route to an internet gateway or NAT, outbound internet traffic is blocked.
Attach an egress-only internet gateway to the private subnet.
Why it's wrong here
Egress-only internet gateways are for IPv6 traffic only.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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: Remove the default route (0.0.0.0/0) pointing to an internet gateway or NAT gateway from the private subnet's route table. — Option C is correct because a route table with only a local route and no internet gateway or NAT gateway prevents outbound internet traffic. Option A is wrong because security groups are stateful and allowing inbound traffic may inadvertently allow outbound responses. Option B is wrong because network ACLs are stateless and need explicit deny rules, but a route-based approach is simpler. Option D is wrong because an egress-only internet gateway is for IPv6, not IPv4.
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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