ANS-C01 Network Design Practice Question
A company has a VPC with a CIDR block of 172.16.0.0/20. They need to create subnets for three tiers: web, application, and database. The web tier must be public and support at least 1000 hosts. The application and database tiers must be private. Which subnet design meets the requirements?
⚠ Common exam trap
The trap here is that candidates often forget to subtract the 5 reserved AWS IPs from the total subnet size, leading them to incorrectly believe a /23 (512 IPs) can support 1000 hosts, or they overlook the non-overlapping subnet requirement in AWS.
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
✓
Web: 172.16.0.0/22, App: 172.16.4.0/24, DB: 172.16.5.0/24
The web tier subnet 172.16.0.0/22 provides 2^(32-22) - 5 = 1024 - 5 = 1019 usable host addresses (AWS reserves 5 IPs per subnet), which meets the requirement of at least 1000 hosts. The application and database subnets use /24 masks, each offering 251 usable hosts, and are private. All subnets fall within the VPC CIDR 172.16.0.0/20 without overlap.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Web: 172.16.0.0/22, App: 172.16.4.0/24, DB: 172.16.5.0/24
Why this is correct
/22 provides 1022 hosts, meeting 1000 requirement.
- ✗
Web: 172.16.0.0/23, App: 172.16.2.0/23, DB: 172.16.4.0/23
Why it's wrong here
/23 provides 510 hosts, not enough.
- ✗
Web: 172.16.0.0/20, App: 172.16.0.0/20, DB: 172.16.0.0/20
Why it's wrong here
Cannot have overlapping subnets.
- ✗
Web: 172.16.0.0/24, App: 172.16.1.0/24, DB: 172.16.2.0/24
Why it's wrong here
/24 only provides 254 hosts, not enough for 1000.
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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.