CCNA Network Infrastructure and Connectivity Practice Question
A subnet uses the prefix /22. How many usable host addresses are available?
⚠ Common exam trap
Remember to subtract the network and broadcast addresses from the total number of addresses to find the usable host count.
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
✓
1022
A /22 leaves 10 host bits available. In plain language, that means each subnet contains 2^10, or 1024, total addresses. Two of those are reserved for the network and broadcast addresses in normal IPv4 subnetting, leaving 1022 usable host addresses. This is a common subnet-capacity calculation. The safest method is to calculate the total address count from the number of host bits and then subtract the two reserved addresses. That leads directly to the correct usable-host value.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
254
Why it's wrong here
The value 254 is the number of usable host addresses in a /24 network, not a /22. With a /22 prefix, the host portion consists of 10 bits, yielding 2^10 - 2 = 1022 usable addresses. Selecting 254 indicates an incorrect assumption that the subnet mask is 255.255.255.0, which corresponds to a /24, and essentially misreads the prefix length as 24 rather than 22.
When this WOULD be correct
If the question specified a /24 subnet instead of /22, the correct calculation would yield 256 total addresses, and after excluding the network and broadcast addresses, there would be 254 usable addresses. Thus, option A would be correct.
- ✗
510
Why it's wrong here
A total of 510 usable hosts is characteristic of a /23 prefix, which reserves only 9 bits for host addressing (2^9 - 2 = 510). In contrast, a /22 prefix leaves 10 host bits, producing 1022 usable addresses. This answer likely stems from a mistake in the bit boundary, possibly recalling the /23 mask of 255.255.254.0 instead of the /22 mask of 255.255.252.0.
When this WOULD be correct
If the question specified a subnet mask of /23 instead of /22, then the calculation would yield 2^(32-23) = 512 total IP addresses, and after subtracting 2 for the network and broadcast addresses, the usable addresses would be 510.
- ✓
1022
Why this is correct
A /22 prefix designates 22 network bits, leaving 10 bits for the host portion of the IPv4 address. This configuration provides 2^10, or 1024, total addresses within the subnet. However, two addresses are always reserved: one for the network address and one for the broadcast address. Subtracting these two reserved addresses from the total yields 1022 usable host addresses, directly satisfying the /22 prefix constraint specified in the question stem.
- ✗
2046
Why it's wrong here
The number 2046 is the usable host count for a /21 prefix, where 11 bits are dedicated to host addressing (2^11 - 2 = 2046). Since a /22 has only 10 host bits, the correct value is 1022 (2^10 - 2). This choice suggests an overestimation of the host space by one bit, perhaps by erroneously calculating using 11 host bits or applying a /21 mask instead of /22.
When this WOULD be correct
If the question specified a /11 subnet instead of /22, the calculation would yield 2^(32-11) = 2048 total addresses, resulting in 2046 usable addresses after accounting for the network and broadcast addresses. In this case, option D would be correct.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓1022Correct answer▾
Why this is correct
A /22 prefix designates 22 network bits, leaving 10 bits for the host portion of the IPv4 address. This configuration provides 2^10, or 1024, total addresses within the subnet. However, two addresses are always reserved: one for the network address and one for the broadcast address. Subtracting these two reserved addresses from the total yields 1022 usable host addresses, directly satisfying the /22 prefix constraint specified in the question stem.
✗254Wrong answer — click to see why▾
Why this is wrong here
A /24 prefix provides 256 total addresses (2^(32-24)=256), with 254 usable host addresses after subtracting the network and broadcast addresses. This does not match the /22 prefix in the question.
★ When this WOULD be the correct answer
If the question specified a /24 subnet instead of /22, the correct calculation would yield 256 total addresses, and after excluding the network and broadcast addresses, there would be 254 usable addresses. Thus, option A would be correct.
Why candidates choose this
Students often confuse /24 with /22 because /24 is a very common subnet size, and they may incorrectly apply the 254 usable host count without calculating the correct number of bits.
✗510Wrong answer — click to see why▾
Why this is wrong here
A /23 prefix provides 512 total addresses (2^(32-23)=512), with 510 usable host addresses. This is half the total addresses of a /22, so it is incorrect for the given prefix.
★ When this WOULD be the correct answer
If the question specified a subnet mask of /23 instead of /22, then the calculation would yield 2^(32-23) = 512 total IP addresses, and after subtracting 2 for the network and broadcast addresses, the usable addresses would be 510.
Why candidates choose this
Some students might mistakenly think that a /22 has 510 usable hosts because they confuse it with a /23, or they may incorrectly calculate the number of host bits.
✗2046Wrong answer — click to see why▾
Why this is wrong here
A /21 prefix provides 2048 total addresses (2^(32-21)=2048), with 2046 usable host addresses. This is double the total addresses of a /22, so it is incorrect for the given prefix.
★ When this WOULD be the correct answer
If the question specified a /11 subnet instead of /22, the calculation would yield 2^(32-11) = 2048 total addresses, resulting in 2046 usable addresses after accounting for the network and broadcast addresses. In this case, option D would be correct.
Why candidates choose this
Students may mistakenly think that a /22 has 2046 usable hosts because they confuse it with a /21, or they may incorrectly add instead of subtract when calculating host bits.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Learn chapter
IPv4 Addressing and Address Classes
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.
Key term
IPv4
IPv4 is the fourth version of the Internet Protocol, a set of rules that assigns unique numerical addresses to devices so they can communicate over networks like the internet.
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