- A
10.0.1.0/24
Why wrong: Subset of existing CIDR, overlaps.
- B
10.1.0.0/16
Non-overlapping, valid addition.
- C
10.0.0.0/8
Why wrong: Overlaps with existing CIDR.
- D
10.0.0.0/16
Why wrong: Same CIDR, not additional.
Question 340 of 1,705
Adding a Non-Overlapping Secondary CIDR to a VPC
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 has a VPC with an IPv4 CIDR of 10.0.0.0/16. They need to add an additional non-overlapping CIDR to the VPC. What is a valid CIDR block they can add?
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
✓
10.1.0.0/16
Option B (10.1.0.0/16) is correct because it is a non-overlapping IPv4 CIDR block that does not conflict with the existing VPC CIDR of 10.0.0.0/16. In AWS, when adding a secondary CIDR to a VPC, the new block must be from the private IP address ranges (RFC 1918) and must not overlap with any existing CIDR blocks in the VPC. The 10.1.0.0/16 range is entirely separate from 10.0.0.0/16, as they are different /16 subnets within the 10.0.0.0/8 space.
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.
- ✗
10.0.1.0/24
Why it's wrong here
Subset of existing CIDR, overlaps.
- ✓
10.1.0.0/16
Why this is correct
Non-overlapping, valid addition.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
10.0.0.0/8
Why it's wrong here
Overlaps with existing CIDR.
- ✗
10.0.0.0/16
Why it's wrong here
Same CIDR, not additional.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume any non-overlapping RFC 1918 block is valid, but they overlook that the new CIDR must not be a subset or superset of the existing CIDR, and AWS specifically requires the new block to be non-overlapping at the VPC level, not just at the subnet level.
Detailed technical explanation
How to think about this question
AWS VPCs support adding up to five secondary IPv4 CIDR blocks, each of which must be from the RFC 1918 ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) or a publicly routable range owned by the customer. The secondary CIDR cannot overlap with any existing CIDR in the VPC, including those from peered VPCs or VPN connections. This allows for expanding the VPC address space without re-architecting, commonly used in multi-account or hybrid cloud scenarios where subnets must be added for new workloads.
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
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.
Visual reference
What to study next
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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: 10.1.0.0/16 — Option B (10.1.0.0/16) is correct because it is a non-overlapping IPv4 CIDR block that does not conflict with the existing VPC CIDR of 10.0.0.0/16. In AWS, when adding a secondary CIDR to a VPC, the new block must be from the private IP address ranges (RFC 1918) and must not overlap with any existing CIDR blocks in the VPC. The 10.1.0.0/16 range is entirely separate from 10.0.0.0/16, as they are different /16 subnets within the 10.0.0.0/8 space.
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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