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Network Management and Operations →mediumMultiple SelectObjective-mapped

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?

A
Check the VPC route table to ensure a route exists for the on-premises CIDR pointing to the virtual private gateway
Correct. The VPC route table must have a route for the on-premises CIDR pointing to the virtual private gateway to route traffic over Direct Connect.
B
Check the VPN connection status to ensure the tunnel is up
Why wrong: Incorrect. Direct Connect uses a virtual private gateway, not a VPN tunnel.
C
Check the security group attached to the EC2 instance to ensure it allows inbound traffic from the on-premises CIDR
Correct. The security group must allow inbound traffic from the on-premises CIDR.
D
Enable VPC Flow Logs and analyze them for dropped packets
Why wrong: Incorrect. VPC Flow Logs are used for post-event analysis, not real-time diagnosis.
E
Check the network ACLs for the subnet to ensure they allow inbound traffic from on-premises
Why wrong: Incorrect. Network ACLs are stateless and require explicit inbound rules for on-premises traffic; they do not automatically allow return traffic. While a misconfigured NACL could cause the issue, the security group is the more common culprit for instance-level filtering.

Full breakdown with real-world context →

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

The correct answers are A and C. For connectivity between an EC2 instance in a public subnet and an on-premises server over AWS Direct Connect, two key checks are: (1) The VPC route table must have a route for the on-premises CIDR pointing to the virtual private gateway (VGW) to route traffic to the Direct Connect connection. (2) The security group attached to the EC2 instance must allow inbound traffic from the on-premises CIDR, as security groups act as a firewall for the instance. Option B is incorrect because Direct Connect uses a virtual private gateway, not a VPN tunnel. Option D is incorrect because VPC Flow Logs are used for analysis, not real-time diagnosis. Option E is incorrect because network ACLs are stateless and typically allow return traffic if outbound rules are permissive; the primary issue is more likely the security group.

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. The VPC route table must have a route for the on-premises CIDR pointing to the virtual private gateway to route traffic over Direct Connect.
Related concept
CIDR notation defines the prefix length.
✗
Check the VPN connection status to ensure the tunnel is up
Why it's wrong here
Incorrect. Direct Connect uses a virtual private gateway, not a VPN tunnel.
✓
Check the security group attached to the EC2 instance to ensure it allows inbound traffic from the on-premises CIDR
Why this is correct
Correct. The security group must allow inbound traffic from the on-premises CIDR.
Related concept
CIDR notation defines the prefix length.
✗
Enable VPC Flow Logs and analyze them for dropped packets
Why it's wrong here
Incorrect. VPC Flow Logs are used for post-event analysis, not real-time diagnosis.
✗
Check the network ACLs for the subnet to ensure they allow inbound traffic from on-premises
Why it's wrong here
Incorrect. Network ACLs are stateless and require explicit inbound rules for on-premises traffic; they do not automatically allow return traffic. While a misconfigured NACL could cause the issue, the security group is the more common culprit for instance-level filtering.

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.

Visual reference

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 — The correct answers are A and C. For connectivity between an EC2 instance in a public subnet and an on-premises server over AWS Direct Connect, two key checks are: (1) The VPC route table must have a route for the on-premises CIDR pointing to the virtual private gateway (VGW) to route traffic to the Direct Connect connection. (2) The security group attached to the EC2 instance must allow inbound traffic from the on-premises CIDR, as security groups act as a firewall for the instance. Option B is incorrect because Direct Connect uses a virtual private gateway, not a VPN tunnel. Option D is incorrect because VPC Flow Logs are used for analysis, not real-time diagnosis. Option E is incorrect because network ACLs are stateless and typically allow return traffic if outbound rules are permissive; the primary issue is more likely the security group.

What should I do if I get this ANS-C01 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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