Count the host bits
IPv4 has 32 bits. Subtract the prefix length to find the host-bit count h.
h = 32 - prefix; addresses = 2^h
[C1, C2]CCNA 200-301 / Free study sprint
Find the subnet. Keep the usable range.
Given an IPv4 address and prefix, identify the network, broadcast and usable host range.
Before you start: Read IPv4 dotted-decimal addresses and understand that a prefix counts network bits.
01 / Start from memory
What would you choose?
Commit to an answer before reading the board.
CCNA 200-301 / IPv4 addressing and subnetting
Find the subnet. Keep the usable range.
Given an IPv4 address and prefix, identify the network, broadcast and usable host range.
01Summary board
The decision path
Find the enclosing block
For /24 through /30, use blocks in the last octet. Round that octet down to a multiple of the block size.
network octet = floor(octet / block) × block
[C1]Reserve both endpoints
The first address identifies the network; the last is the broadcast. Hosts lie strictly between them.
broadcast = network + block - 1
[C1, C2]Worked example / Original StudyMaps scenario
A host is configured as 192.168.8.77/27
Find its subnet and the address range available for ordinary LAN hosts.
.64Network.65 to .94Usable hosts.95Broadcast
- 32 - 27 = 5 host bits; 2^5 = 32 addresses.
- Last-octet blocks begin at 0, 32, 64, 96... The value 77 falls in the 64-95 block.
- Network: 192.168.8.64/27. Broadcast: 192.168.8.95.
- Exclude .64 and .95: usable hosts are .65 through .94, a total of 30.
Result192.168.8.65 to 192.168.8.94 are usable.
Principles: [C1, C2]. Original example: StudyMaps.03 / Apply it
Your turn.
Three new problems. Explain your choice on paper, then check the reasoning.
0 of 3 practice problems checked
04 / Return later
Does it still make sense tomorrow?
Bookmark this page and try the new problem without the board. This is a practice check, not an exam-readiness score.
Open the return-later problem
Sources and scope
Conventional IPv4 LAN subnets, /24 through /30. /31 point-to-point and /32 host routes use different rules. Focused CCNA practice supplement; it does not cover the full exam blueprint.
- [C1] Cisco: Configure IP Addresses and Unique SubnetsChecked 2026-09-09 · Prefix notation, subnet boundaries, reserved endpoints and /31 exceptions.
- [C2] Cisco: Understand Host and Subnet QuantitiesChecked 2026-09-09 · Host bits, address counts and ordinary usable-host counts.
- [C3] Cisco CCNA v1.1 exam topicsChecked 2026-09-09 · Exam topic 1.6: configure and verify IPv4 addressing and subnetting.
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