ANS-C01 Network Management and Operations Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. 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 a VPC with a CIDR of 10.0.0.0/16. They have two subnets: 10.0.1.0/24 (public) and 10.0.2.0/24 (private). An EC2 instance in the private subnet needs to download patches from the internet. The team creates a NAT gateway in the public subnet and updates the private subnet route table to route 0.0.0.0/0 to the NAT gateway. The EC2 instance still cannot reach the internet. The team confirms the NAT gateway has an elastic IP and the public subnet has an internet gateway. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network ACL for the private subnet denies outbound traffic to the internet.
The security group or network ACL of the private subnet may be blocking outbound traffic. However, a common mistake is not disabling source/destination check on the NATgateway. But NAT gateway is a managed service, so source/destination check is automatically disabled. Option A is correct: the private subnet's network ACL must allow outbound traffic and inbound return traffic. Option B is not needed because NAT gateway is managed. Option C is not a requirement. Option D would be for the NAT gateway's subnet.
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 private subnet route table does not have a route for the NAT gateway's IP.
The public subnet does not have a route to the internet gateway.
Why it's wrong here
Public subnet must have that route; but issue is from private subnet.
✗
The NAT gateway does not have source/destination check disabled.
Why it's wrong here
NATgateway is managed; source/destination check is disabled by default.
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: The network ACL for the private subnet denies outbound traffic to the internet. — The security group or network ACL of the private subnet may be blocking outbound traffic. However, a common mistake is not disabling source/destination check on the NAT gateway. But NAT gateway is a managed service, so source/destination check is automatically disabled. Option A is correct: the private subnet's network ACL must allow outbound traffic and inbound return traffic. Option B is not needed because NAT gateway is managed. Option C is not a requirement. Option D would be for the NAT gateway's subnet.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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