The correct answer is to check the operating system firewall and web server configuration on the EC2 instance. This is because a successful ping confirms that Layer 3 routing and the network path are working correctly, including the Direct Connect private VIF and the VPC’s route tables, but a TCP connection failure points to a higher-layer issue. Since the security group already permits inbound TCP port 80 from the on-premises CIDR, the blockage must be at the instance level—either the OS firewall (like iptables or Windows Firewall) is dropping the traffic, or the web server itself is not listening on port 80. On the ANS-C01 exam, this scenario tests your ability to isolate connectivity problems across the OSI model, a common trap being to overcomplicate with BGP or NACLs when ping works. Remember the memory tip: “Ping is Layer 3, TCP is Layer 4—if ping passes but TCP fails, look at the host, not the net.”
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 uses AWS Direct Connect with a private virtual interface (VIF) to connect its on-premises network to its VPC. The on-premises network team reports that they can ping the private IP address of an EC2 instance in the VPC, but cannot establish a TCP connection to a web server running on that instance. The network security group allows inbound TCP port 80 from the on-premises CIDR. What should the network engineer check next?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the operating system firewall and web server configuration on the EC2 instance.
Option C is correct because the instance's OS firewall or web server configuration may be blocking the connection. Option A is wrong because ping works, indicating routing is fine. Option B is wrong because the BGP session status is unrelated to connectivity to the instance. Option D is wrong because the NACL is stateless and would affect ping as well.
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.
✗
Review the network ACL associated with the subnet to ensure it allows inbound TCP 80.
Why it's wrong here
NACL would affect ping too if it were blocking.
✓
Check the operating system firewall and web server configuration on the EC2 instance.
Why this is correct
The OS firewall or application may block TCP despite security group allowing it.
Check the BGP session status on the Direct Connect virtual interface.
Why it's wrong here
BGP is not related to TCP connectivity to the instance.
✗
Verify the route table on the VPC has a route back to the on-premises network.
Why it's wrong here
Ping works, so routing is functional.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: Check the operating system firewall and web server configuration on the EC2 instance. — Option C is correct because the instance's OS firewall or web server configuration may be blocking the connection. Option A is wrong because ping works, indicating routing is fine. Option B is wrong because the BGP session status is unrelated to connectivity to the instance. Option D is wrong because the NACL is stateless and would affect ping as well.
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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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.
Question Discussion
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