IPv4 addressing
What an IPv4 address is, how dotted notation maps to binary, which ranges are private (RFC 1918), what 127.0.0.1 and 169.254.x.x mean, and how devices get addresses.
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Addressing
IPv4, subnetting, IPv6, NAT
Subnetting & CIDR
What subnetting is, how CIDR notation works, and how to calculate any subnet by hand: with worked examples, a live subnet calculator, comparison tables and FAQ.
IPv6 addressing
IPv6 addressing: eight hex groups, mercifully shortened. Part of the free Link to NetEra networking curriculum.
NAT & private ranges
NAT & private ranges: private in, public out, one address for the house. Part of the free Link to NetEra networking curriculum.