A network engineer is assigned the IPv4 block 10.100.0.0/21 to create subnetworks for regi… — Cisco CCNA

A network engineer is assigned the IPv4 block $10.100.0.0/21$ to create subnetworks for regional offices. Each regional office network requires a $/26$ subnet mask. How many $/26$ subnetworks can be created from this $10.100.0.0/21$ block?

Answer: 32 subnets

Answer

32 subnets can be created from the

10.100.0.0/21

block.

Subtracting the original prefix length (

/21

) from the new subnet prefix length (

/26

) yields

5

subnet bits (

26 - 21 = 5

). Calculating

2^5

gives

32

subnets available within the

10.100.0.0/21

parent block.

Step-by-Step Solution

Determine the number of subnet bits borrowed by subtracting the initial block prefix length from the target subnet prefix length.

Borrowed bits =

26 - 21 = 5

bits.

The difference between the new prefix length and the original prefix length represents the bits available to create subnets.

Calculate the total number of subnets using

2^n

, where

n

is the number of borrowed bits.

2^5 = 32

subnets.

Each additional bit assigned to the network prefix doubles the number of valid subnets.

Key Concept

Calculating Subnet Count from CIDR Prefix Differences

Estimated Time:1m 30s

Question

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