The correct answer is to create a separate route table for each Availability Zone and associate only the subnets within that AZ to it, ensuring the route tables contain only the local VPC CIDR route. This works because AWS’s underlying network infrastructure inherently routes traffic locally within an AZ when the destination IP falls within the same VPC CIDR, and by isolating the route tables per AZ you prevent any explicit or propagated routes that could force traffic across AZ boundaries. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of VPC routing fundamentals and the default behavior of local routes—a common trap is assuming a single shared route table is sufficient, but that would allow cross-AZ traffic to still use the local route, which actually keeps it within the VPC but does not guarantee it stays within the same AZ. A useful memory tip is “one table per AZ keeps traffic at home”—think of each AZ as its own neighborhood with its own local map, and you never add a shortcut that leads to another neighborhood.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 designing a VPC with multiple subnets across three Availability Zones. The application requires that all traffic between subnets within the same AZ stay within that AZ to minimize latency and data transfer costs. Which configuration achieves this?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Use a single route table for all subnets and add specific routes for each AZ.
Why wrong: Does not guarantee intra-AZ routing.
B
Use an AWS Transit Gateway with separate attachments for each AZ.
Why wrong: Transit gateway routes traffic centrally, not necessarily within the same AZ.
C
Create a VPC peering connection between subnets in the same AZ.
Why wrong: Unnecessary and doesn't control routing.
D
Create a route table for each AZ and associate the subnets in that AZ with the route table. Ensure the route tables have only local routes for the VPC CIDR.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a route table for each AZ and associate the subnets in that AZ with the route table. Ensure the route tables have only local routes for the VPC CIDR.
Option A is correct. By creating separate route tables for each AZ and ensuring that routes for other AZs use the local route (which keeps traffic within the VPC), traffic between subnets in the same AZ will stay within the AZ because AWS uses local routing within the same AZ by default. Option B is wrong because a single route table would not segregate traffic by AZ. Option C is wrong because VPC peering is for cross-VPC. Option D is wrong because a transit gateway would route traffic centrally, not necessarily keep it within the AZ.
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.
✗
Use a single route table for all subnets and add specific routes for each AZ.
Why it's wrong here
Does not guarantee intra-AZ routing.
✗
Use an AWS Transit Gateway with separate attachments for each AZ.
Why it's wrong here
Transit gateway routes traffic centrally, not necessarily within the same AZ.
✗
Create a VPC peering connection between subnets in the same AZ.
Why it's wrong here
Unnecessary and doesn't control routing.
✓
Create a route table for each AZ and associate the subnets in that AZ with the route table. Ensure the route tables have only local routes for the VPC CIDR.
Why this is correct
Local routing within the same AZ is used.
Clue confirmation
The clue word "minimum / minimize" 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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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 Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a route table for each AZ and associate the subnets in that AZ with the route table. Ensure the route tables have only local routes for the VPC CIDR. — Option A is correct. By creating separate route tables for each AZ and ensuring that routes for other AZs use the local route (which keeps traffic within the VPC), traffic between subnets in the same AZ will stay within the AZ because AWS uses local routing within the same AZ by default. Option B is wrong because a single route table would not segregate traffic by AZ. Option C is wrong because VPC peering is for cross-VPC. Option D is wrong because a transit gateway would route traffic centrally, not necessarily keep it within the AZ.
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: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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