The answer is that SSH traffic is allowed from all IP addresses. This is correct because NACLs are stateless and rules are evaluated in ascending order by rule number; once a rule matches, evaluation stops and no further rules are considered. Rule 100 explicitly permits all SSH traffic, so rule 200’s deny and rule 300’s more specific allow are never reached, making the subnet open to SSH from any source. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of NACL rule evaluation order and stateless behavior, a common trap being that students assume a later deny rule overrides an earlier allow—it does not, since NACLs process rules sequentially and stop at the first match. Remember the key difference: security groups are stateful and evaluate all rules, while NACLs are stateless and use first-match logic. A useful memory tip is “first match wins, stateless means no return traffic tracking.”
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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
A security engineer reviews the NACL entries above for a subnet. Which statement about incoming SSH traffic (port 22) is correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SSH traffic is allowed from all IP addresses.
NACLs are stateless and rules are evaluated in order by rule number. Rule 100 allows SSH from all IPs. Rule 200 denies SSH from all IPs, but it is not evaluated because rule 100 already allowed. Rule 300 allows SSH from 10.0.0.0/8 but is not reached. Since rule 100 allows all, SSH is allowed from all IPs. Option A is correct.
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.
✗
SSH traffic is allowed only from the 10.0.0.0/8 range.
Why it's wrong here
Rule 100 allows all; rule 300 is not evaluated.
✓
SSH traffic is allowed from all IP addresses.
Why this is correct
Rule 100 allows all SSH traffic; subsequent rules are not evaluated.
SSH traffic is allowed from 10.0.0.0/8 and denied from all others.
Why it's wrong here
Rule 100 allows all, so traffic from outside 10.0.0.0/8 is also allowed.
✗
SSH traffic is denied from all IP addresses.
Why it's wrong here
Rule 100 allows it, so it is not denied.
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 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: SSH traffic is allowed from all IP addresses. — NACLs are stateless and rules are evaluated in order by rule number. Rule 100 allows SSH from all IPs. Rule 200 denies SSH from all IPs, but it is not evaluated because rule 100 already allowed. Rule 300 allows SSH from 10.0.0.0/8 but is not reached. Since rule 100 allows all, SSH is allowed from all IPs. Option A is correct.
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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