You have a VPC with CIDR block 172.16.0.0/16. You want to create two subnets without overlapping IPs. Which pair of CIDR blocks is valid?

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AWS - VPC Fundamentals

You have a VPC with CIDR block 172.16.0.0/16. You want to create two subnets without overlapping IPs. Which pair of CIDR blocks is valid?

A172.16.0.0/17 and 172.16.128.0/17

B172.16.0.0/18 and 172.16.64.0/17

C172.16.0.0/16 and 172.16.0.0/17

D172.16.0.0/15 and 172.16.128.0/17

Step-by-Step Solution

Solution:

Step 1: Understand the VPC range
172.16.0.0/16 covers IPs from 172.16.0.0 to 172.16.255.255.
Step 2: Check subnet ranges for overlap
/17 splits the /16 into two halves: 172.16.0.0 to 172.16.127.255 and 172.16.128.0 to 172.16.255.255. These do not overlap.
Final Answer:
172.16.0.0/17 and 172.16.128.0/17 -> Option A
Quick Check:
Non-overlapping halves split /16 into two /17s [OK]

Quick Trick: Split CIDR by increasing prefix to avoid overlap [OK]

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