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220-1201 Practice Question: A technician is setting up a new office network…
A technician is setting up a new office network with 50 devices. The network must support growth up to 100 devices. The technician chooses a subnet mask of 255.255.255.0. How many usable host addresses does this subnet provide?
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Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
254
A subnet mask of 255.255.255.0 (or /24) provides 256 total addresses, with 254 usable for hosts (the first address is the network ID and the last is the broadcast address). This is sufficient for the current 50 devices and allows for growth up to 100, but not beyond 254.
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Option-by-option breakdown
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- ✓
254
Why this is correct
A /24 subnet mask (255.255.255.0) indicates that the first 24 bits are used for the network portion, leaving 8 bits for host addresses. With 8 host bits, there are 2^8 = 256 possible IP addresses within that subnet. However, the first address (all host bits zero) is reserved as the network address, and the last address (all host bits one) is reserved as the broadcast address. Therefore, 256 - 2 = 254 usable host addresses remain for devices.
- ✗
255
Why it's wrong here
The number 255 is often associated with the last octet of a subnet mask (e.g., 255.255.255.0) or the broadcast address for a /24 network (e.g., x.y.z.255). While 255 is part of the total address range, it does not represent the number of *usable* host addresses. Specifically, the broadcast address, which ends in 255 for a /24, is one of the two addresses reserved and thus cannot be assigned to a host.
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256
Why it's wrong here
A /24 subnet provides 2^8, or 256, total possible IP addresses within its range. This count includes all addresses from the network address (e.g., x.y.z.0) up to the broadcast address (e.g., x.y.z.255). However, network protocols dictate that the network address itself and the broadcast address for that specific subnet cannot be assigned to individual hosts, making 256 an inaccurate count for *usable* hosts.
- ✗
128
Why it's wrong here
The number 128 would be relevant for a /25 subnet mask (255.255.255.128), which leaves 7 bits for host addresses. In that scenario, 2^7 = 128 total addresses are available. After reserving one for the network address and one for the broadcast address, a /25 subnet would yield 126 usable host addresses, not 128. Therefore, 128 is incorrect for a /24 subnet and also not the usable count for a /25.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.