Internet Protocol version 6 (IPv6) is the successor to IPv4, designed to solve IPv4 address exhaustion with a 128-bit address space (340 undecillion addresses). Unlike IPv4's 32-bit addresses, IPv6 fundamentally redesigns packet headers for efficiency, mandates IPsec support, and integrates autoconfiguration directly into the protocol through Stateless Address Autoconfiguration (SLAAC) and Neighbor Discovery Protocol (NDP). Understanding IPv6 is critical for modern networking: address representation rules differ significantly from IPv4, with hexadecimal notation, compression rules, and prefix-based subnetting replacing traditional subnet masks. The most important concept to internalize is that every interface always has multiple addresses simultaneously—link-local for local communication, global unicast for internet routing, and often temporary privacy addresses—all coexisting on the same interface.