hardMultiple ChoiceObjective-mapped
220-1201 Practice Question: Is designing a subnet scheme for a company with…
A network engineer is designing a subnet scheme for a company with three departments: Sales (50 devices), HR (20 devices), and IT (10 devices). The company uses the 10.0.0.0/24 network. To minimize waste, the engineer decides to use variable-length subnet masking (VLSM). Which of the following subnet masks should be assigned to the Sales department?
⚠ Common exam trap
The 220-1201 exam often tests the candidate's ability to calculate the exact number of usable hosts per subnet (2^(32-prefix)-2) and match it to the requirement, tricking those who forget to subtract the network and broadcast addresses or who round up to the nearest power of two without considering the -2.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
255.255.255.192
The Sales department requires 50 hosts. A /26 subnet mask (255.255.255.192) provides 62 usable addresses (2^(32-26)-2 = 62), which is the smallest subnet that can accommodate 50 devices without waste. VLSM allows using this mask within the 10.0.0.0/24 network, leaving room for other subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
255.255.255.128
Why it's wrong here
This subnet mask, equivalent to a /25 CIDR, reserves 7 bits for host addresses, yielding 2^7 = 128 total addresses. After deducting the network and broadcast addresses, 126 usable IP addresses remain. While sufficient for 50 devices, this allocation results in 76 unused addresses, representing significant waste and inefficient use of the IP address space, especially in larger network designs.
- ✓
255.255.255.192
Why this is correct
The subnet mask 255.255.255.192 corresponds to a /26 CIDR, which designates 6 host bits. This configuration provides 2^6 = 64 total IP addresses within the subnet. Subtracting the network and broadcast addresses leaves 62 usable host addresses, which perfectly accommodates the requirement for 50 devices with minimal address waste, making it the most efficient choice.
- ✗
255.255.255.224
Why it's wrong here
This subnet mask, represented as a /27 CIDR, allocates 5 bits for host addresses. Consequently, it creates a subnet with 2^5 = 32 total IP addresses. After accounting for the mandatory network and broadcast addresses, only 30 usable host addresses are available, which is insufficient to support the required 50 devices.
- ✗
255.255.255.240
Why it's wrong here
A subnet mask of 255.255.255.240, or a /28 CIDR, designates only 4 bits for host addresses. This results in a total of 2^4 = 16 IP addresses for the entire subnet. With two addresses reserved for network and broadcast, only 14 usable host addresses remain, which is drastically inadequate for a requirement of 50 devices.
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Related to this question
Learn chapter
Network Configuration: IP, DNS, DHCP
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
Key term
Classless Inter-domain Routing
Classless Inter-domain Routing (CIDR) is a method for allocating IP addresses and routing IP packets more efficiently by replacing the old class-based system with variable-length subnet masks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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