A network engineer is allocated the IPv4 address block 10.240.16.0/20 to create subnets fo… — CompTIA Network+

A network engineer is allocated the IPv4 address block $10.240.16.0/20$ to create subnets for distinct department segments. Each segment requires a minimum of $120$ usable host IP addresses. What is the maximum number of subnets of this minimum required size that can be created from the given block?

Answer: 32 subnets

Answer

The maximum number of subnets of the minimum required size that can be created is 32.

To support a minimum of 120 hosts, 7 host bits are required (

2^7 - 2 = 126 \ge 120

). A subnet with 7 host bits has a prefix length of

/25

(

32 - 7 = 25

). Partitioning a

/20

block into

/25

subnets borrows 5 bits (

25 - 20 = 5

), resulting in

2^5 = 32

subnets.

Step-by-Step Solution

Calculate the host bits required for the minimum host capacity requirement

7 host bits are required because

2^7 - 2 = 126 \ge 120

Using 6 host bits only provides

2^6 - 2 = 62

usable addresses, which fails to meet the 120 host requirement.

Calculate the required subnet mask prefix length

The prefix length is

/25

, calculated as

32 - 7 = 25

Subtracting host bits from the 32 total IPv4 address bits determines the network prefix.

Calculate the total subnets formed by splitting a

/20

block into

/25

subnets

2^{25 - 20} = 2^5 = 32

subnets.

The number of subnets created is 2 raised to the power of the borrowed subnet bits.

Key Concept

IPv4 Subnetting and Host Capacity Calculation

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