The answer is that the route table of the subnet where the Client VPN endpoint is attached does not have a route to the VPC CIDR. This is the most likely cause because when a Client VPN endpoint is associated with a subnet, that subnet’s route table must include a route pointing to the VPC’s CIDR block, with the target set to the VPN endpoint’s network interface. Without this route, traffic from the client can reach the endpoint but cannot be forwarded to any VPC resources, even if the security group and authorization rules are correctly configured. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how Client VPN integrates with VPC routing—a common trap is assuming split-tunneling or security groups are at fault, when the real issue is a missing route in the subnet’s route table. Remember the memory tip: “VPN connects, but resources are unreachable? Check the subnet route table for the VPC CIDR route.”
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 is implementing an AWS Client VPN endpoint to provide remote access to its VPC resources. The company's on-premises network uses a split-tunneling configuration to route only corporate traffic through the VPN. The Client VPN endpoint is associated with a single subnet in the VPC. Users report that they can connect to the Client VPN but cannot reach resources in the VPC. The Client VPN endpoint's security group allows all traffic. What is the MOST likely cause of this issue?
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 route table of the subnet where the Client VPN endpoint is attached does not have a route to the VPC CIDR.
Option D is correct because the subnet's route table must have a route pointing to the Client VPN endpoint for traffic to reach VPC resources. Option A is incorrect because split-tunneling does not cause this issue. Option B is incorrect because authorization rules are separate from security groups. Option C is incorrect because the Client VPN endpoint uses its own security group.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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 security group associated with the Client VPN endpoint does not allow inbound traffic from the client CIDR.
Why it's wrong here
The security group is for the endpoint itself, not for traffic to VPC.
✗
The authorization rules do not grant access to the target subnets.
Why it's wrong here
Authorization rules control access, but not routing.
✓
The route table of the subnet where the Client VPN endpoint is attached does not have a route to the VPC CIDR.
Why this is correct
Without a route, traffic from clients won't reach VPC resources.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The Client VPN endpoint is configured with full-tunneling instead of split-tunneling.
Why it's wrong here
Full-tunneling would route all traffic through VPN, not prevent access.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
→Do not assume successful login means full administrative access.
→Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
→Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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 Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related ANS-C01 questions on access control and AAA configuration.
Network Implementation — This question tests Network Implementation — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: The route table of the subnet where the Client VPN endpoint is attached does not have a route to the VPC CIDR. — Option D is correct because the subnet's route table must have a route pointing to the Client VPN endpoint for traffic to reach VPC resources. Option A is incorrect because split-tunneling does not cause this issue. Option B is incorrect because authorization rules are separate from security groups. Option C is incorrect because the Client VPN endpoint uses its own security group.
What should I do if I get this ANS-C01 question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related ANS-C01 questions on access control and AAA configuration.
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?
Authentication checks who the user is.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is setting up an AWS Client VPN endpoint for remote access. Users report they can connect to the VPN but cannot access resources in the VPC. The VPN endpoint is associated with a subnet that has a route table with a route to an internet gateway. The security group for the VPN endpoint allows all traffic. What could be the issue?
easy
✓ A.The route table associated with the VPN subnet does not have a route to the VPC CIDR
B.The authorization rules for the VPN endpoint do not include the VPC CIDR
C.The security group for the VPN endpoint does not allow outbound traffic
D.The client CIDR range overlaps with the VPC CIDR
Why A: Option C is correct because the route table associated with the VPN subnet must have a route to the VPC CIDR via the VPN endpoint's network interface. Option A is wrong because authorization rules are for user access, not routing. Option B is wrong because client CIDR allocation is for VPN IPs. Option D is wrong because security group allows all traffic.
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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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