CCNA Network Infrastructure and Connectivity Practice Question
A host is configured as 10.10.20.190/26. Which range contains usable host addresses for that subnet?
⚠ Common exam trap
Be careful not to include the network and broadcast addresses as usable host addresses. Always calculate the subnet boundaries accurately.
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
✓
10.10.20.129 to 10.10.20.190
A /26 uses blocks of 64 addresses. In plain language, the ranges are 0–63, 64–127, 128–191, and 192–255. Since the host ends in 190, it belongs to the 128–191 block. In that block, 10.10.20.128 is the network address and 10.10.20.191 is the broadcast address. That leaves 10.10.20.129 through 10.10.20.190 as the usable host range. This question checks whether you can identify the correct block and then exclude the reserved endpoints properly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
10.10.20.129 to 10.10.20.190
Why this is correct
A /26 prefix length yields a 64-address block. Since the address 10.10.20.128 falls on a 64-byte boundary, the subnet's network address is 10.10.20.128 and its broadcast address is 10.10.20.191. Therefore, the usable host addresses are exactly 10.10.20.129 through 10.10.20.190, as this excludes the network and broadcast identifiers while including every valid host in that range.
- ✗
10.10.20.128 to 10.10.20.191
Why it's wrong here
This range erroneously includes the network address 10.10.20.128 and the broadcast address 10.10.20.191. On a /26 subnet, the network and broadcast addresses cannot be assigned to hosts, so the usable host range must start at .129 and end at .190. Thus, the provided range is too broad because it covers all addresses in the block rather than only the assignable host addresses.
When this WOULD be correct
If the question asked for the range of addresses in the subnet 10.10.20.128/26, then option B would be correct, as it would include all usable addresses from 10.10.20.129 to 10.10.20.190, while still including the network and broadcast addresses.
- ✗
10.10.20.130 to 10.10.20.191
Why it's wrong here
This option incorrectly excludes the valid host address 10.10.20.129, which is the first usable address in the 10.10.20.128/26 subnet. Additionally, it includes the broadcast address 10.10.20.191, which cannot be assigned to a host. Consequently, the range is simultaneously too narrow—by omitting one legitimate host—and too broad—by including the broadcast address.
When this WOULD be correct
If the question specified a subnet mask of /25 instead of /26, then option C would be correct, as the usable host range would then be 10.10.20.129 to 10.10.20.254, allowing for addresses up to 10.10.20.191.
- ✗
10.10.20.193 to 10.10.20.254
Why it's wrong here
A /26 subnet has a block size of 64 addresses. The subnet containing the address 10.10.20.128 is 10.10.20.128/26, which runs from .128 to .191. The range 10.10.20.193 to 10.10.20.254 belongs to the next /26 subnet, 10.10.20.192/26, whose network address is .192 and broadcast is .255, so it is a completely separate subnet and does not include any hosts from the 10.10.20.128/26 subnet.
When this WOULD be correct
If the question specified a different subnet, such as 10.10.20.192/26, then option D would be correct, as it would contain usable addresses from 10.10.20.193 to 10.10.20.254 for that subnet.
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.
✓10.10.20.129 to 10.10.20.190Correct answer▾
Why this is correct
A /26 prefix length yields a 64-address block. Since the address 10.10.20.128 falls on a 64-byte boundary, the subnet's network address is 10.10.20.128 and its broadcast address is 10.10.20.191. Therefore, the usable host addresses are exactly 10.10.20.129 through 10.10.20.190, as this excludes the network and broadcast identifiers while including every valid host in that range.
✗10.10.20.128 to 10.10.20.191Wrong answer — click to see why▾
Why this is wrong here
Option B is incorrect because it includes the network address (10.10.20.128) and the broadcast address (10.10.20.191) for the subnet 10.10.20.128/26, which are not usable host addresses.
★ When this WOULD be the correct answer
If the question asked for the range of addresses in the subnet 10.10.20.128/26, then option B would be correct, as it would include all usable addresses from 10.10.20.129 to 10.10.20.190, while still including the network and broadcast addresses.
Why candidates choose this
Candidates may choose this option because it appears to include a broader range of addresses, and they might mistakenly believe it encompasses usable addresses without recognizing the significance of the network and broadcast addresses.
✗10.10.20.130 to 10.10.20.191Wrong answer — click to see why▾
Why this is wrong here
Option C is incorrect because the subnet mask /26 indicates a subnet range of 10.10.20.128 to 10.10.20.191, but the usable host addresses are from 10.10.20.129 to 10.10.20.190, excluding the network and broadcast addresses.
★ When this WOULD be the correct answer
If the question specified a subnet mask of /25 instead of /26, then option C would be correct, as the usable host range would then be 10.10.20.129 to 10.10.20.254, allowing for addresses up to 10.10.20.191.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of subnetting, confusing the usable range with the total range of addresses, or miscalculating the subnet boundaries.
✗10.10.20.193 to 10.10.20.254Wrong answer — click to see why▾
Why this is wrong here
Option D is incorrect because the range 10.10.20.193 to 10.10.20.254 falls outside the subnet defined by 10.10.20.190/26, which only allows for usable addresses from 10.10.20.130 to 10.10.20.190.
★ When this WOULD be the correct answer
If the question specified a different subnet, such as 10.10.20.192/26, then option D would be correct, as it would contain usable addresses from 10.10.20.193 to 10.10.20.254 for that subnet.
Why candidates choose this
Candidates may be tempted by option D because it includes addresses that are numerically close to the given host address, leading to confusion about the correct subnet range.
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
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
Go deeper
Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
Network address
A network address is a unique identifier that allows devices to find and communicate with each other on a computer network.
Key term
Broadcast address
A broadcast address is a special network address used to send data to every device on a local network segment simultaneously.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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