The most likely cause is that the VPC route table has a more specific route pointing to the VPN connection. This occurs because AWS route tables evaluate the most specific prefix match, so even when the Direct Connect link is healthy, a route with a longer subnet mask (e.g., /24) to the VPN will override a less specific route (e.g., /16) to the Direct Connect virtual private gateway. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of route priority and BGP propagation in hybrid networks, often appearing as a trap where engineers assume Direct Connect is always preferred. The key insight is that route specificity beats gateway type—a more precise VPN route will always win, regardless of connection health. Remember the mnemonic: “Specificity over stability” to recall that prefix length, not link reliability, dictates traffic flow in VPC route selection.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 has a hybrid network with an AWS Direct Connect connection to a VPC. They also have a site-to-site VPN connection as a backup. The VPC routing tables are configured with a route to the on-premises CIDR via the virtual private gateway. The network engineer notices that traffic from the VPC to on-premises is not using the Direct Connect connection even when it is healthy. 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 table has a more specific route pointing to the VPN connection
Option A is correct because when both Direct Connect and VPN are configured, the VPC route table typically has a single route to the on-premises CIDR via the virtual private gateway. Without more specific routing, the VPN BGP route may be preferred depending on route propagation and prefix matching. Option B is wrong because the VPN connection being down would not cause traffic to avoid Direct Connect. Option C is wrong because the Direct Connect virtual interface must be in the 'Available' state to pass traffic. Option D is wrong because the AWS Site-to-Site VPN connection uses a virtual private gateway or transit gateway, not a Customer Gateway as the target.
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 VPC route table has a more specific route pointing to the VPN connection
Why this is correct
If the VPNBGP route is more specific (e.g., /24 vs /16), it will take precedence over the static route to Direct Connect.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
If the VPN is down, traffic would be routed via Direct Connect if the route exists.
✗
The VPN connection is attached to a Customer Gateway
Why it's wrong here
The VPN attaches to a Customer Gateway, but the route target is the virtual private gateway or transit gateway.
✗
The Direct Connect virtual interface is in the 'Down' state
Why it's wrong here
If the virtual interface were down, Direct Connect would not be functional, but the question states it is healthy.
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 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 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 table has a more specific route pointing to the VPN connection — Option A is correct because when both Direct Connect and VPN are configured, the VPC route table typically has a single route to the on-premises CIDR via the virtual private gateway. Without more specific routing, the VPN BGP route may be preferred depending on route propagation and prefix matching. Option B is wrong because the VPN connection being down would not cause traffic to avoid Direct Connect. Option C is wrong because the Direct Connect virtual interface must be in the 'Available' state to pass traffic. Option D is wrong because the AWS Site-to-Site VPN connection uses a virtual private gateway or transit gateway, not a Customer Gateway as the target.
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.
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