In creating the next generation Internet Protocol, the IETF has also created a transition path from IPv4 to IPv6. The immense size of the Internet, and thus all the users of IPv4, makes an overnight change impossible. And no user can afford any down-time caused by waiting to upgrade.
For these reasons, the transition to IPv6 can be done on a node-by-node basis. Autoconfiguration should help by eliminating the need for human intervention to configure systems.
There are features of IPv6 that are compatible with IPv4, which will help ease the transition. For example, IPv4 addresses can be embedded within IPv6 addresses and all IPv6 nodes, at least for the time being, also support IPv4. Packets for IPv6 can be embedded within IPv4 packets so tunneling through parts of the network that support only IPv4 is possible.
Because of this compatibility between IPv4 and IPv6, some users may not feel the need to upgrade. However, the benefits of using IPv6 far outweigh the cost of upgrading. To not upgrade would be like riding a horse on the Autobahn rather than driving a car.
IPv6 is being tested over and over by IETF and its participating partners. With its core specifications finalized, IPv6 implementations should occur within a year and Internet Service Providers should begin to offer IPv6 links during the next three to four years.