Subnet mask to host capacity: With subnet mask 255.255.255.224, what is the maximum number of IP host addresses available on a single subnet?
Networking
Subnetting
Difficulty: Easy
Choose an option
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A14
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B15
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C16
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D30
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E62
Answer
Correct Answer: 30
Explanation
Introduction / Context:Calculating usable hosts from a subnet mask is foundational for IP addressing design. The /27 mask (255.255.255.224) is a frequent example in certification exams.
Given Data / Assumptions:
- Subnet mask: 255.255.255.224 (/27)
- We want usable host addresses per subnet (excludes network and broadcast)
Concept / Approach:Usable hosts per subnet = 2^(host_bits) - 2. For /27, there are 32 - 27 = 5 host bits.
Step-by-Step Solution:
host_bits = 32 - 27 = 5total addresses = 2^5 = 32usable hosts = 32 - 2 = 30Verification / Alternative check:Block size of /27 is 32 addresses. Removing the network and broadcast leaves 30 hosts.
Why Other Options Are Wrong:
- 14/15/16: Correspond to smaller subnets (/28 or miscounting usable hosts).
- 62: That is typical of a /26 (64 addresses total minus 2).
Common Pitfalls:Forgetting to subtract 2 for network and broadcast; mixing up /27 with /28 calculations.
Final Answer:30