Question

Difficulty: MediumIPv4 Addressing and Subnetting

A network administrator is designing an IPv4 addressing scheme for a enterprise WLAN segment that must support at least $500$ usable host devices per subnet. What is the maximum CIDR prefix length (integer value of the mask bits) that can be assigned to meet this requirement without wasting IP address space?

Answer: 23

Answer

The maximum CIDR prefix length that supports at least 500 usable host addresses is 23.

To host at least

500

usable devices, a subnet requires 9 host bits because

2^9 - 2 = 510

usable IP addresses. Subtracting 9 host bits from the 32 total bits in an IPv4 address results in a prefix length of 23.

Step-by-Step Solution

1

Calculate the required number of host bits

9 host bits are required.

Using the formula

2^h - 2

, 8 host bits yield only 254 usable addresses, whereas 9 host bits yield

510

usable addresses, which satisfies the

500

host minimum requirement.

2

Calculate the network prefix length in CIDR notation

The prefix length is 23.

An IPv4 address consists of 32 bits in total. Subtracting the 9 host bits (

32 - 9

) leaves 23 bits for the network and subnet identifier.

Key Concept

IPv4 Host Capacity and CIDR Prefix Calculation

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Topics

IPv4 Addressing and Subnetting

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