- A
The route table in the VPN VPC has a default route (0.0.0.0/0) pointing to the Network Firewall, but the Network Firewall's route table needs a route back to the VPN VPC for the client CIDR, which is missing.
For traffic to flow, the inspection VPC must have a route back to the VPN VPC for the client CIDR. If the Network Firewall's route table (or the inspection VPC's route table) does not have a route for the client CIDR pointing to the VPN VPC's attachment (e.g., Transit Gateway), return traffic is dropped.
- B
The client certificate is not associated with the same CA as the server certificate, causing TLS handshake failure.
Why wrong: If authentication failed, users would not be able to connect. The stem says users can connect, so TLS handshake is successful.
- C
The subnet route table in the VPN VPC does not have a route for the client CIDR (assigned by the VPN) pointing to the VPN endpoint's network interface.
Why wrong: The VPN endpoint automatically handles routing for the client CIDR. The route table in the VPN VPC needs a route for the client CIDR to the VPN endpoint's ENI, but this is typically added automatically. However, if missing, return traffic would not reach clients. But the issue is clients cannot access internal resources, not that they cannot receive responses.
- D
The AWS Network Firewall in the inspection VPC is blocking traffic from the VPN client CIDR because it does not have a rule allowing it.
Why wrong: The Network Firewall might be blocking traffic, but the stem says centralized inspection VPC. However, the most common issue is that the route table in the VPN VPC is not sending traffic to the Network Firewall correctly.
Quick Answer
The answer is a missing return route in the Network Firewall’s route table for the VPN client CIDR. While the VPN VPC correctly sends all traffic to the Network Firewall via a default route, the firewall itself must have a route pointing back to the VPN VPC’s subnet to forward inspected traffic to internal resources. Without this return path, packets from clients are dropped at the firewall, causing connectivity failure despite successful VPN authentication and authorization rules. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of asymmetric routing in centralized inspection architectures—a common trap where engineers focus only on the outbound path. Remember that stateful firewalls require symmetric traffic flows; if the firewall cannot route replies back to the client CIDR, the connection fails. A quick memory tip: “Outbound is half the story; the return route is the other half.”
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 company is using AWS Client VPN for remote access. They want to ensure that only clients with a valid client certificate can connect, and that traffic is routed through a centralized inspection VPC. The VPN endpoint is configured with mutual authentication using server and client certificates. The route table in the VPN VPC has a default route pointing to an AWS Network Firewall endpoint in the inspection VPC. Users report that they can connect to the VPN but cannot access any internal resources. The network engineer checks the Client VPN endpoint configuration and confirms that the authorization rules allow access to the internal CIDR (10.0.0.0/8). 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 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
The route table in the VPN VPC has a default route (0.0.0.0/0) pointing to the Network Firewall, but the Network Firewall's route table needs a route back to the VPN VPC for the client CIDR, which is missing.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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.
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 route table in the VPN VPC has a default route (0.0.0.0/0) pointing to the Network Firewall, but the Network Firewall's route table needs a route back to the VPN VPC for the client CIDR, which is missing.
Why this is correct
For traffic to flow, the inspection VPC must have a route back to the VPN VPC for the client CIDR. If the Network Firewall's route table (or the inspection VPC's route table) does not have a route for the client CIDR pointing to the VPN VPC's attachment (e.g., Transit Gateway), return traffic is dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
- ✗
The client certificate is not associated with the same CA as the server certificate, causing TLS handshake failure.
Why it's wrong here
If authentication failed, users would not be able to connect. The stem says users can connect, so TLS handshake is successful.
- ✗
The subnet route table in the VPN VPC does not have a route for the client CIDR (assigned by the VPN) pointing to the VPN endpoint's network interface.
Why it's wrong here
The VPN endpoint automatically handles routing for the client CIDR. The route table in the VPN VPC needs a route for the client CIDR to the VPN endpoint's ENI, but this is typically added automatically. However, if missing, return traffic would not reach clients. But the issue is clients cannot access internal resources, not that they cannot receive responses.
- ✗
The AWS Network Firewall in the inspection VPC is blocking traffic from the VPN client CIDR because it does not have a rule allowing it.
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: The route table in the VPN VPC has a default route (0.0.0.0/0) pointing to the Network Firewall, but the Network Firewall's route table needs a route back to the VPN VPC for the client CIDR, which is missing.
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.
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Last reviewed: Jun 20, 2026
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