- A
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.0.0/25, 10.0.1.0/25, 10.0.2.0/25
Why wrong: Overlap with public subnets.
- B
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24
Non-overlapping, three AZs each.
- C
Public: 10.0.0.0/24, 10.0.2.0/24, 10.0.4.0/24; Private: 10.0.1.0/24, 10.0.3.0/24, 10.0.5.0/24
Non-overlapping, each /24 in different AZ.
- D
Public: 10.0.0.0/24, 10.0.0.0/25, 10.0.0.128/25; Private: 10.0.1.0/24, 10.0.1.0/25, 10.0.1.128/25
Why wrong: Overlapping CIDRs within same AZ.
- E
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.0.0/25, 10.0.1.0/25, 10.0.2.0/25
Why wrong: Overlaps with public subnets.
Question 196 of 1,705
Subnet CIDR Allocation — Non-Overlapping Subnets for High Availability | AWS Advanced Networking Specialty Explained
This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 deploying a VPC with a CIDR block of 10.0.0.0/16. The VPC requires six subnets: three public and three private, each with a /24 CIDR. The company needs to ensure high availability across three Availability Zones. Which TWO of the following are valid subnet CIDR assignments that meet these requirements?
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
✓
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24
Option B is correct because it assigns six non-overlapping /24 subnets (10.0.0.0/24 through 10.0.5.0/24) within the 10.0.0.0/16 VPC, allowing three public and three private subnets to be distributed across three Availability Zones for high availability. Option C is also correct as it uses the same six /24 subnets but interleaves public and private ranges (e.g., public: 10.0.0.0/24, 10.0.2.0/24, 10.0.4.0/24; private: 10.0.1.0/24, 10.0.3.0/24, 10.0.5.0/24), which still provides non-overlapping /24 CIDRs and supports the required multi-AZ architecture.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.0.0/25, 10.0.1.0/25, 10.0.2.0/25
Why it's wrong here
Overlap with public subnets.
- ✓
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24
Why this is correct
Non-overlapping, three AZs each.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Public: 10.0.0.0/24, 10.0.2.0/24, 10.0.4.0/24; Private: 10.0.1.0/24, 10.0.3.0/24, 10.0.5.0/24
Why this is correct
Non-overlapping, each /24 in different AZ.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Public: 10.0.0.0/24, 10.0.0.0/25, 10.0.0.128/25; Private: 10.0.1.0/24, 10.0.1.0/25, 10.0.1.128/25
Why it's wrong here
Overlapping CIDRs within same AZ.
- ✗
Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.0.0/25, 10.0.1.0/25, 10.0.2.0/25
Why it's wrong here
Overlaps with public subnets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume subnets can share the same base IP range as long as the subnet mask differs, but AWS requires all subnets in a VPC to have non-overlapping CIDR blocks regardless of prefix length.
Detailed technical explanation
How to think about this question
In AWS, subnets within a VPC must have non-overlapping CIDR blocks; overlapping ranges cause routing conflicts and prevent proper network segmentation. The /24 subnet mask provides 256 IP addresses (251 usable after AWS reserves 5), while a /25 provides 128 IP addresses (123 usable). When designing for high availability across three Availability Zones, each subnet must be placed in a different AZ, and the CIDR blocks must be distinct to avoid IP address duplication, which is why interleaving public and private subnets (as in Option C) is a valid pattern as long as the ranges do not overlap.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Public: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24; Private: 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24 — Option B is correct because it assigns six non-overlapping /24 subnets (10.0.0.0/24 through 10.0.5.0/24) within the 10.0.0.0/16 VPC, allowing three public and three private subnets to be distributed across three Availability Zones for high availability. Option C is also correct as it uses the same six /24 subnets but interleaves public and private ranges (e.g., public: 10.0.0.0/24, 10.0.2.0/24, 10.0.4.0/24; private: 10.0.1.0/24, 10.0.3.0/24, 10.0.5.0/24), which still provides non-overlapping /24 CIDRs and supports the required multi-AZ architecture.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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