These notes outline the rationale, stages, and mechanisms for the transition from Internet Protocol version 4 (IPv4) to Internet Protocol version 6 (IPv6). They present a phased deployment path from isolated IPv6 “islands” to native IPv6, and ultimately to IPv6 dominance, while emphasizing coexistence for a prolonged period. The notes reviews dual-stack operation, tunneling, and translation, then details carrier-grade approaches such as Dual-Stack Lite (DS-Lite), Address plus Port (A+P), and NAT64/DNS64. Adoption snapshots (as of October 2023) and implementation readiness are provided to contextualize timelines and constraints. The core driver is address space depletion; there is no official “switch-off” date, so the migration proceeds incrementally and smoothly where feasible.
The target characteristics of the IPv4→IPv6 transition are “incremental, seamless, [and] smooth.”
The plan rests on three pillars: a dual-stack approach (IPv6 as a new layer-3 protocol alongside IPv4, with systems generating or receiving v6 or v4 as needed), address mapping, and mechanisms for tunneling and translation. This sets the stage for a long coexistence period in which both protocols operate in parallel.
The deployment is shown as four steps:
Initial isolated IPv6 networks with IPv6-in-IPv4 tunnels and dual-stack hosts.
Growing IPv6 islands with IPv6-only hosts, dual-stack, and translating devices.
Native IPv6 connectivity with translation as needed.
IPv6 predominance, with residual IPv4 segments and IPv4-in-IPv6 tunnels.
Protocol specifications have been in place since 1996, with implementations on routers (including hardware layer-3 switches, albeit sometimes with fewer features or reduced stability compared with IPv4) and on major operating systems (Windows since 2000; Unix variants such as Ubuntu, Debian, FreeBSD; and macOS). Adoption data (Google, October 2023) cite ~45% global IPv6, ~48% in the U.S., ~15% in Italy, and ~75% in France/Germany. There is no official switch-off date; the shift remains gradual, driven primarily by address space depletion.
IPv4 and IPv6 will coexist at least for a while.