Subnetting
Dividing one IP network into smaller subnetworks to improve organization and reduce broadcast traffic.
Subnetting divides a single IP block into smaller subnetworks by borrowing bits from the host portion. Each borrowed bit doubles the subnet count while halving hosts per subnet. Usable hosts equal 2^h − 2, where h is the remaining host bits; the two reserved addresses are the network address and the directed broadcast. On the N10-009 exam, questions give a host requirement and ask for the correct CIDR prefix. A common trap is picking the prefix that fits exactly — a /27 yields just 30 hosts for a 30-host need, leaving no growth room. Verify 2^h − 2 meets or exceeds the requirement.
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