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Difficulty: EasyIPv4 Addressing and Subnetting

A network administrator is creating a new subnet dedicated to a small group of administrative servers using the IPv4 prefix length /28/28. What is the maximum number of usable host IP addresses available for devices within this subnet?

  1. 14Answer
  2. B
    16
  3. C
    15
  4. D
    30

Answer

14 usable host IP addresses
With a /28/28 prefix, 44 bits remain for the host portion (32−28=432 - 28 = 4). The total number of IP addresses is 24=162^4 = 16. Because the network address (all host bits 0) and the broadcast address (all host bits 1) cannot be assigned to hosts, subtracting 22 yields exactly 1414 usable host IP addresses.

Step-by-Step Solution

1
Determine the number of host bits
32−28=432 - 28 = 4 host bits
An IPv4 address consists of 3232 bits. Subtracting the prefix length leaves the host portion of the address.
2
Calculate total IP addresses in the subnet
24=162^4 = 16 total IP addresses
The total number of IP addresses in a CIDR block is calculated as 2host bits2^{\text{host bits}}.
3
Subtract reserved addresses to find usable host IP count
16−2=1416 - 2 = 14 usable host IPs
The first address (network ID) and the last address (broadcast address) cannot be assigned to individual host interfaces.

Key Concept

IPv4 Subnet Usable Host Capacity Calculation
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Topics

IPv4 Addressing and Subnetting

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