The answer is to check VPC Flow Logs to identify the source IP addresses and review the security group rules to ensure they are not permitting the unwanted SSH traffic. VPC Flow Logs capture IP traffic metadata for network interfaces, allowing you to pinpoint the exact source IPs generating the unwanted SSH traffic, while security group rules act as a virtual firewall at the instance level and must be inspected to confirm they are not inadvertently allowing the offending CIDR ranges. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your ability to differentiate between stateful security groups and stateless network ACLs, a common trap where candidates mistakenly check NACLs first or look at route tables, which only affect outbound traffic. Remember the memory tip: "Flow logs find the foe, security groups stop the show" — always start with flow logs to identify the source, then verify the security group rules to block the traffic.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 security engineer notices that an EC2 instance in a public subnet is receiving inbound SSH traffic from a range of IP addresses that should be blocked. Which two actions should the engineer take to troubleshoot? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Review the Security Group rules attached to the instance
Options A and D are correct. Checking VPC Flow Logs helps identify the source IP of the traffic. Reviewing Security Group rules ensures that the security group is not allowing the unwanted SSH traffic. Option B is wrong because Network ACLs are stateless and might be blocking, but they are not the first place to check for inbound traffic to an instance. Option C is wrong because the route table does not affect inbound traffic to the instance. Option E is wrong because the instance metadata does not contain network access rules.
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.
✗
Check the instance metadata for IP restrictions
Why it's wrong here
Instance metadata does not contain network ACL or security group information.
✗
Check the route table associated with the subnet
Why it's wrong here
Route tables do not affect inbound traffic to the instance.
✓
Review the Security Group rules attached to the instance
Why this is correct
Security groups control inbound traffic to the instance.
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 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
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: Review the Security Group rules attached to the instance — Options A and D are correct. Checking VPC Flow Logs helps identify the source IP of the traffic. Reviewing Security Group rules ensures that the security group is not allowing the unwanted SSH traffic. Option B is wrong because Network ACLs are stateless and might be blocking, but they are not the first place to check for inbound traffic to an instance. Option C is wrong because the route table does not affect inbound traffic to the instance. Option E is wrong because the instance metadata does not contain network access rules.
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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