A network engineer is assigned the IPv4 network block 10.140.0.0/18 to provision subnets f… — Cisco CCNA

A network engineer is assigned the IPv4 network block $10.140.0.0/18$ to provision subnets for standard branch offices. Each branch office requires a subnet capable of accommodating at least $110$ usable host IP addresses. What is the maximum number of equal-sized subnets supporting this host requirement that can be created from the $10.140.0.0/18$ block?

Answer: 128 subnets

Answer

The maximum number of valid branch subnets that can be created is 128.

To support at least 110 usable hosts per subnet, 7 host bits are required (

2^7 - 2 = 126

usable hosts). Subtracting 7 host bits from 32 total IPv4 bits results in a

/25

prefix length. Borrowing bits from the allocated

/18

summary block gives

25 - 18 = 7

subnet bits. Therefore,

2^7 = 128

valid subnets can be created.

Step-by-Step Solution

Determine the required host bits for at least 110 usable host IP addresses.

7 host bits are required because

2^7 - 2 = 126 \ge 110

, whereas 6 host bits (

2^6 - 2 = 62

) are insufficient.

Every IPv4 subnet reserves two IP addresses for the network ID and the broadcast ID, making the usable host formula

2^h - 2

Determine the required CIDR prefix length for each subnet.

The prefix length is

/25

(

32 - 7 = 25

An IPv4 address consists of 32 bits; subtracting the 7 host bits leaves 25 network bits.

Calculate the number of borrowed subnet bits relative to the parent block.

7 subnet bits are borrowed (

25 - 18 = 7

Extending the parent network prefix from

/18

/25

borrows 7 bits for subnetting.

Calculate the total number of

/25

subnets within the

/18

parent block.

The total number of subnets is

2^7 = 128

Borrowing

n

subnet bits yields

2^n

distinct subnets.

Key Concept

Calculating IPv4 subnet capacity and prefix derivation based on host requirements

Estimated Time:2m 0s

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