IPv6 is the next-generation Internet protocol that replaces IPv4. It features a 128-bit address size allowing for many more IP addresses compared to IPv4's 32-bit addresses. IPv6 also includes improvements in routing, network autoconfiguration, security, quality of service, and extensibility. A transition from IPv4 to IPv6 is underway using mechanisms like dual stacking that allow both protocols to coexist on networks. While not yet widely deployed, IPv6 is expected to fully replace IPv4 in the coming years.