ANS-C01 VPC Secondary CIDR Practice Question
A company has a VPC with a CIDR block of 10.0.0.0/16. It needs to create a secondary CIDR block for additional subnets that must not overlap with the existing CIDR. Which CIDR block should be used?
⚠ Common exam trap
The ANS-C01 exam often tests whether candidates know that secondary CIDRs can be from the same RFC 1918 class as the primary as long as they do not overlap. Many mistakenly eliminate D (10.1.0.0/16) because it is in the 10.0.0.0/8 range, but it is actually valid. Both A and D are acceptable.
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
✓
172.16.0.0/16
Both A (172.16.0.0/16) and D (10.1.0.0/16) are correct because they are private, non-overlapping secondary CIDRs. The primary CIDR is 10.0.0.0/16; any non-overlapping CIDR is valid, regardless of RFC 1918 class. Options B and C overlap with the primary and therefore cannot be used.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
172.16.0.0/16
Why this is correct
Correct: 172.16.0.0/16 is a private, non-overlapping CIDR from a different RFC 1918 block.
- ✗
10.0.0.0/16
Why it's wrong here
Incorrect: 10.0.0.0/16 is identical to the primary CIDR and would overlap completely.
- ✗
10.0.0.0/8
Why it's wrong here
Incorrect: 10.0.0.0/8 overlaps with the primary 10.0.0.0/16 because the /8 includes the /16 range.
- ✓
10.1.0.0/16
Why this is correct
Correct: 10.1.0.0/16 is within the same 10.0.0.0/8 range but does not overlap with the primary 10.0.0.0/16, making it a valid secondary CIDR.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.