2Addressing and Subnet Formats

• 2.1Private and public addresses

  Covers the difference between a globally unique, internet-routable public address and a private address reused inside an organization (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), the makeup of address classes A/B/C, the APIPA block (169.254.0.0/16) that appears when DHCP fails, and NAT that translates private to public—as the foundation for telling whether an address can reach the outside.

• 2.2IPv4 addresses and subnet formats

  Covers the idea of a subnet that divides a network into smaller pieces, the subnet mask that decides "how much of an address is the network portion," its correspondence with slash (CIDR) notation counting the mask's one bits, the fact that each subnet reserves its first address as the network address and its last as the broadcast address, and the router's role of separating broadcast domains—learned with gentle /24 and /25 examples (no complex calculation).

• 2.3IPv6 addresses and prefix formats

  Covers the main address types in 128-bit IPv6—the globally unique global unicast (GUA, 2000::/3), the link-only link-local (fe80::/10), the internal unique local (ULA, fc00::/7), and the self-referring loopback (::1)—the meaning of the common /64 prefix, and the fact that IPv6 has no broadcast and replaces it with multicast (ff00::/8), as the foundation for telling address types apart.