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CompTIA Network+ (N10-009)Network SecurityHard

A network architect is segmenting a flat 10.20.0.0/22 network into four equally sized VLANs to isolate departments, with each VLAN needing to be a valid, non-overlapping subnet. What subnet mask should be assigned to each new VLAN?

  1. A/26
  2. B/24
  3. C/25
  4. D/23
Show answer & explanation

Correct answer: B. /24

A /22 network contains 1,024 total addresses (2^(32-22) = 1024). Splitting it into 4 equal subnets means 1024 ÷ 4 = 256 addresses per subnet, which corresponds to a /24 mask (2^(32-24) = 256). A /23 would only yield 2 subnets, and /25 or /26 would create more than four subnets each smaller than required.

Why the other options are wrong

  • A. A /26 provides only 64 addresses per subnet, creating 16 subnets instead of 4.
  • C. A /25 provides only 128 addresses per subnet, creating 8 subnets instead of 4.
  • D. A /23 provides 512 addresses per subnet, yielding only 2 subnets from the /22 block.

Subnetting for Segmentation

Dividing a larger block into equal subnets requires calculating total addresses in the block and dividing by the desired number of segments to determine the correct mask.

  • /22 = 2^(32-22) = 1024 total addresses
  • Dividing by number of desired subnets gives subnet size
  • Match resulting size to correct CIDR mask (256 addresses = /24)

Memory trick: 1024 divided by 4 departments equals 256 each — that's a /24.

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