The answer is to check route tables, security group rules, and network ACLs. When a Site-to-Site VPN tunnel is established but traffic is not flowing, the issue almost always lies in the routing or firewall layers: the route tables in the VPC must include a route pointing to the on-premises network via the virtual private gateway, while security groups and network ACLs must explicitly permit the desired traffic in both inbound and outbound directions. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of the layered security model and the distinction between stateful security groups and stateless network ACLs—a common trap is assuming the tunnel status alone guarantees connectivity, or mistakenly thinking a NAT gateway or internet gateway is required for VPN traffic. Remember the mnemonic “RSA” for Routes, Security groups, and ACLs to quickly recall the three critical checks when troubleshooting Site-to-Site VPN traffic not flowing.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 setting up a Site-to-Site VPN connection between an on-premises network and AWS. The VPN tunnel is established, but traffic is not flowing. Which THREE configuration items should be checked?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Route tables in the VPC and on-premises router.
Option A is correct because route tables must have routes to the remote network. Option C is correct because security group rules must allow traffic. Option E is correct because network ACLs must allow traffic. Option B is incorrect because a NATgateway is not required for VPN. Option D is incorrect because an internet gateway is not needed for VPN traffic.
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.
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.
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 Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Route tables in the VPC and on-premises router. — Option A is correct because route tables must have routes to the remote network. Option C is correct because security group rules must allow traffic. Option E is correct because network ACLs must allow traffic. Option B is incorrect because a NAT gateway is not required for VPN. Option D is incorrect because an internet gateway is not needed for VPN traffic.
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.
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 →
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 configuring a site-to-site VPN connection between its on-premises network and AWS. The VPN tunnel is up, but traffic is not passing. The company has verified that routes are correct on both sides. Which TWO actions should the company take to troubleshoot the issue?
hard
A.Verify that the virtual private gateway is attached to the VPC.
B.Ensure that the on-premises firewall is configured to allow IPSec traffic.
✓ C.Check the security group rules for the EC2 instances in the VPC.
D.Verify that the VPN tunnel is using the correct encryption algorithm.
✓ E.Check the network ACLs for the subnets.
Why C: Options A and D are correct because checking security group and NACL rules is essential for traffic flow. B is irrelevant as tunnel is up. C is not applicable. E is already done.
Last reviewed: Jun 20, 2026
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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.
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