Which IPv4 prefix matches each usable host range?
DRAG DROP Drag and drop the IPv4 network subnets from the left onto the correct usable host ranges on the right. Select and Place: [sampleXML/xmlfile-8_1.png]
Community Insight
You must compute each subnet's network and broadcast addresses from the prefix length, and the trap is assuming the right-hand ranges are all derived from one subnet rather than from five separate masks.
This drag-and-drop asks you to pair the host address 172.28.228.144 written with five different prefix lengths (/18, /21, /23, /25, /29) to the usable host range that subnet would produce. The page confirms the correct mapping and shows the block-size math behind each pair.
Learners match by eyeballing the first three octets or by copying a partially correct community post, forgetting that the network address is found by zeroing host bits and the broadcast by setting all host bits, so only first and last usable addresses count.
Community Discussion (12 comments)
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Expert Analysis
Why the Answer Is Correct
For each prefix you zero out the host bits of 172.28.228.144 to get the network, then set all host bits to get the broadcast, and report network+1 through broadcast-1. A /18 uses 255.255.192.0, giving 172.28.192.0–172.28.255.255, so the usable range is 172.28.192.1–172.28.255.254; a /21 uses 255.255.248.0, giving 172.28.224.0–172.28.231.255, so usable is 172.28.224.1–172.28.231.254. The /23 (255.255.254.0) spans 172.28.228.0–172.28.229.255, so usable is 172.28.228.1–172.28.229.254; the /25 falls in the upper half of the last octet (128–255), giving 172.28.228.129–172.28.228.254; and the /29 block of 8 starting at 144 yields 172.28.228.145–172.28.228.150. Each range's host count also confirms it: 16382, 2046, 510, 126, and 6 usable hosts respectively.Why Other Candidate Answers Are Wrong
One posted mapping lists the /21 range as 172.28.224.1–172.28.255.254 and the /23 as 172.28.228.1–172.28.255.254, which mixes up the /21 block of 8 with the /18 block of 64 and assumes the /23 runs to the end of the third octet. Another post extends the /29 to 172.28.228.151, which is the broadcast address and therefore never usable, and it contradicts its own earlier correct six-host listing. Treating the left side as literal network numbers instead of a single host written with different masks leads to ranges that start at 172.28.228.144 itself, which would wrongly include the network address. Matching by host count alone without checking the start address also fails, because ranges like /21 and /23 differ in both bounds.Community Comment Notes
Several commenters converged on the same correct table, including paniaguavo and anoop4487, who both listed all five pairs exactly as derived above. ExG2 and jhhhrwy described shortcut methods—counting the span in the last octet to find 2^7 = 128 for the /25, and using 2^3-2 = 6 hosts for the /29—which produce the correct answers. Request7108 pointed out the wording is awkward, noting it "should be what network range would be if it were in a /18, /21, etc.," while Garfieldcat observed that "those IP are addresses instead of subnet numbers." As wince_gusty suggested, counting usable hosts on the right side and mapping them to the prefix length is the fastest approach under exam time pressure.Official Reference
Exam Strategy
Work the right side first: count the usable hosts (or the block size in the varying octet) and let that identify the prefix length, since a 16382-host range can only be a /18 and a 6-host range can only be a /29. Always verify the start is network+1 and the end is broadcast-1 before placing a tile.
Frequently Asked Questions
How do I find the usable host range for 172.28.228.144 with a /21 mask?
A /21 mask is 255.255.248.0, so the block size is 8 in the third octet. 172.28.224.0 is the network and 172.28.231.255 the broadcast, making the usable range 172.28.224.1-172.28.231.254.
Why is the /29 range only 172.28.228.145 to 172.28.228.150?
A /29 has 3 host bits, giving 8 addresses total; 172.28.228.144 is the network and .151 is the broadcast. Subtracting both leaves 6 usable hosts from .145 to .150.
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