The answer is the absence of a VPC route for the on-premises CIDR pointing to the virtual private gateway (VGW). This is the classic cause of asymmetric routing in a Direct Connect setup: the on-premises network can reach the VPC because BGP advertises the VPC CIDR successfully, but return traffic from the VPC has no explicit route directing it back through the VGW, so it either drops or takes an unintended path. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how route propagation from a VGW works—specifically that the VGW does not automatically add routes to your VPC route tables; you must either manually add a static route or enable route propagation. A common trap is assuming that because BGP is exchanging routes and on-premises traffic arrives, the reverse path is automatically configured. Remember the memory tip: “BGP brings routes in, but VPC tables need a push”—the VGW propagates routes only if you explicitly enable it in the VPC route table.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 on-premises network and an Amazon VPC over an AWS Direct Connect connection. The on-premises network uses BGP to advertise routes to the VPC. The VPC is associated with a virtual private gateway (VGW). The on-premises network can reach resources in the VPC, but VPC resources cannot reach on-premises resources. 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 VPC route tables do not have a route for the on-premises CIDR pointing to the virtual private gateway.
Option C is correct because if the VPC's route tables do not have a route pointing to the virtual private gateway for the on-premises CIDR, traffic from the VPC will not be sent over the Direct Connect. Option A is incorrect because BGP is used for route exchange; if on-premises can reach VPC, BGP is working. Option B is incorrect because security groups are stateful and allow return traffic. Option D is incorrect because the virtual private gateway needs to propagate routes to VPC route tables.
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 virtual private gateway is not attached to the VPC.
Why it's wrong here
If it were not attached, on-premises could not reach VPC either.
✗
The BGP session is not established.
Why it's wrong here
If on-premises can reach VPC, BGP must be working.
✗
The security group associated with the VPC resources is blocking inbound traffic from on-premises.
Why it's wrong here
Security groups are stateful; if outbound traffic from VPC is allowed, return traffic is automatically allowed.
✓
The VPC route tables do not have a route for the on-premises CIDR pointing to the virtual private gateway.
Why this is correct
Without a route, VPC traffic destined for on-premises will not be routed to the Direct Connect.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 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: The VPC route tables do not have a route for the on-premises CIDR pointing to the virtual private gateway. — Option C is correct because if the VPC's route tables do not have a route pointing to the virtual private gateway for the on-premises CIDR, traffic from the VPC will not be sent over the Direct Connect. Option A is incorrect because BGP is used for route exchange; if on-premises can reach VPC, BGP is working. Option B is incorrect because security groups are stateful and allow return traffic. Option D is incorrect because the virtual private gateway needs to propagate routes to VPC route tables.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.