Valid host check for /22: Given subnet 172.16.17.0/22, which of the following is a valid host address (with mask shown)?
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A172.16.17.1 255.255.255.252
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B172.16.0.1 255.255.240.0
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C172.16.20.1 255.255.254.0
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D172.16.18.255 255.255.252.0
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E172.16.19.255 255.255.255.0
Answer
Correct Answer: 172.16.18.255 255.255.252.0
Explanation
Introduction / Context:Verifying a valid host requires matching both the IP's range within the subnet and the correct subnet mask. /22 networks often confuse because the broadcast address ends with .255, yet some middle .255 values can still be hosts.
Given Data / Assumptions:
- Subnet: 172.16.17.0/22
- /22 mask = 255.255.252.0
- We must pick an IP/mask pair that is valid within this /22.
Concept / Approach:A /22 spans 4 contiguous /24s. Determine the network range, then confirm the candidate address falls within it and isn’t the network or broadcast address.
Step-by-Step Solution:
/22 block size in third octet = 4. The 17.x subnet belongs to the 16–19 range.Network: 172.16.16.0/22; Broadcast: 172.16.19.255.Candidate D: 172.16.18.255 with 255.255.252.0 is within 16.0–19.255 and is not the broadcast (which is 19.255).Verification / Alternative check:Check each option's mask and range: only option D pairs the correct /22 mask and an IP inside the range without being network/broadcast.
Why Other Options Are Wrong:
- A: Mask is /30 and not the specified /22.
- B: IP and mask point to a different network entirely.
- C: Mask /23 and IP 20.x fall outside 16–19 range for the /22 given.
- E: Mask /24; also 19.255 would be the /24 broadcast if /24 were used, but the mask is wrong.
Common Pitfalls:Assuming any .255 is always a broadcast; it only is when it matches the subnet’s actual broadcast boundary.
Final Answer:172.16.18.255 255.255.252.0