The answer is to enable VPC Flow Logs, publish them to CloudWatch Logs, and create a CloudWatch metric filter for SSH traffic. This works because VPC Flow Logs capture metadata about IP traffic, including source/destination ports, and when published to CloudWatch Logs, a metric filter can parse those logs for port 22 entries, automatically generating a custom metric that triggers a CloudWatch Alarm for alerting—all without deploying additional infrastructure. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of operational overhead versus capability: Security Groups can deny SSH but cannot alert, AWS Config tracks configuration changes not traffic, and GuardDuty detects threats but lacks a native SSH-specific filter. A common trap is choosing GuardDuty for its threat detection name, but remember that VPC Flow Logs plus a metric filter give you precise, low-overhead traffic pattern detection. Memory tip: "Flow to Filter to Alarm" — the three-step chain for any port-specific traffic alert.
ANS-C01 Network Management and Operations Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 a VPC with public and private subnets. The security team wants to detect and alert on any SSH traffic (port 22) that originates from the internet to any EC2 instance in the VPC. Which solution achieves this with minimal operational overhead?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable VPC Flow Logs, publish to CloudWatch Logs, and create a metric filter for SSH traffic.
VPC Flow Logs can be published to CloudWatch Logs, and a CloudWatch Logs filter metric can detect SSH traffic. Security Groups can deny traffic but not alert. AWS Config can track configuration changes. GuardDuty detects threats but not specifically SSH traffic alerts.
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.
✓
Enable VPC Flow Logs, publish to CloudWatch Logs, and create a metric filter for SSH traffic.
Why this is correct
This approach logs traffic and alerts on SSH without manual inspection.
Configure a security group rule to deny inbound SSH and enable security group logging.
Why it's wrong here
Security groups deny traffic but do not provide configurable alerts.
✗
Use AWS Config to detect security group rules that allow SSH from 0.0.0.0/0.
Why it's wrong here
AWS Config evaluates configuration, not real-time traffic.
✗
Enable Amazon GuardDuty and rely on its threat detection.
Why it's wrong here
GuardDuty detects threats but does not provide a specific alert for any SSH traffic.
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 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 Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Enable VPC Flow Logs, publish to CloudWatch Logs, and create a metric filter for SSH traffic. — VPC Flow Logs can be published to CloudWatch Logs, and a CloudWatch Logs filter metric can detect SSH traffic. Security Groups can deny traffic but not alert. AWS Config can track configuration changes. GuardDuty detects threats but not specifically SSH traffic alerts.
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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