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Question

Difficulty: EasyIPv4 Addressing and Subnetting

A network technician is configuring a local subnetwork for a department that requires a /27/27 prefix length. How many usable host IPv4 addresses can be assigned to devices within this subnetwork?

Answer: 30 addresses

Answer

There are 30 usable host IPv4 addresses in a /27 subnet.
A /27 prefix leaves 5 host bits (32−27=532 - 27 = 5). Calculating 252^5 gives 3232 total IP addresses. Subtracting 22 reserved addresses for the network ID and broadcast address results in exactly 3030 usable host IPv4 addresses.

Step-by-Step Solution

1
Determine the number of host bits remaining in a /27 CIDR prefix.
32 total bits - 27 network bits = 5 host bits.
An IPv4 address contains 32 bits divided between network bits and host bits.
2
Calculate the total capacity of IP addresses for 5 host bits.
2^5 = 32 total IP addresses.
The number of total IP addresses in a subnet is calculated using 2 raised to the power of the host bits.
3
Subtract the reserved network and broadcast addresses.
32 - 2 = 30 usable host addresses.
The lowest IP address represents the network ID and the highest IP address represents the broadcast address, neither of which can be assigned to host devices.

Key Concept

IPv4 Usable Host Address Calculation
Estimated Time:45s
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Topics

IPv4 Addressing and Subnetting

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