- A
Check the VPC route table to ensure a route exists for the on-premises CIDR pointing to the virtual private gateway
Correct routing is essential.
- B
Check the VPN connection status to ensure the tunnel is up
Why wrong: This is a Direct Connect scenario, not VPN.
- C
Check the security group attached to the EC2 instance to ensure it allows inbound traffic from the on-premises CIDR
Security groups are stateful; inbound rules must allow traffic.
- D
Enable VPC Flow Logs and analyze them for dropped packets
Why wrong: Flow logs are useful but not the first step for real-time diagnosis.
- E
Check the network ACLs for the subnet to ensure they allow inbound traffic from on-premises
Why wrong: NACLs are stateless; if outbound traffic is allowed, return traffic is also allowed.
Quick Answer
The answer is to check the route tables for the EC2 instance’s subnet and verify the security group allows inbound traffic from the on-premises CIDR. When an EC2 instance in a public subnet can reach the internet but not an on-premises server over Direct Connect, the issue is typically a missing route pointing the on-premises CIDR to the virtual private gateway, or a security group rule blocking the inbound traffic. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how traffic flows through a VPC: outbound internet traffic uses an internet gateway, while on-premises traffic must be explicitly routed to the Direct Connect virtual private gateway. A common trap is assuming network ACLs are the culprit, but they are stateless and automatically allow return traffic if properly configured; security groups, however, are stateful and require an explicit inbound rule. For a quick memory tip, remember “Route then Secure” — always verify the route table first for the on-premises path, then check the security group for the inbound allow.
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 network engineer is troubleshooting connectivity issues between an Amazon EC2 instance in a public subnet and an on-premises server over AWS Direct Connect. The instance can reach the internet but cannot reach the on-premises server. Which TWO actions should the engineer take to diagnose the issue?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Check the VPC route table to ensure a route exists for the on-premises CIDR pointing to the virtual private gateway
Options B and D are correct. Checking route tables verifies that the on-premises CIDR is pointing to the virtual private gateway. Checking security groups ensures inbound traffic from on-premises is allowed. Option A is incorrect because NACLs are stateless and usually allow return traffic if properly configured. Option C is incorrect because flow logs are for logging, not real-time diagnosis. Option E is incorrect because the VPN is not involved.
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 VPC route table to ensure a route exists for the on-premises CIDR pointing to the virtual private gateway
Why this is correct
Correct routing is essential.
Related concept
CIDR notation defines the prefix length.
- ✗
Check the VPN connection status to ensure the tunnel is up
Why it's wrong here
This is a Direct Connect scenario, not VPN.
- ✓
Check the security group attached to the EC2 instance to ensure it allows inbound traffic from the on-premises CIDR
Why this is correct
Security groups are stateful; inbound rules must allow traffic.
Related concept
CIDR notation defines the prefix length.
- ✗
Enable VPC Flow Logs and analyze them for dropped packets
Why it's wrong here
Flow logs are useful but not the first step for real-time diagnosis.
- ✗
Check the network ACLs for the subnet to ensure they allow inbound traffic from on-premises
Why it's wrong here
NACLs are stateless; if outbound traffic is allowed, return traffic is also allowed.
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.
Trap categories for this question
Scenario analysis trap
This is a Direct Connect scenario, not VPN.
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: Check the VPC route table to ensure a route exists for the on-premises CIDR pointing to the virtual private gateway — Options B and D are correct. Checking route tables verifies that the on-premises CIDR is pointing to the virtual private gateway. Checking security groups ensures inbound traffic from on-premises is allowed. Option A is incorrect because NACLs are stateless and usually allow return traffic if properly configured. Option C is incorrect because flow logs are for logging, not real-time diagnosis. Option E is incorrect because the VPN is not involved.
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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Last reviewed: Jun 20, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
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