IPv6 is short for "Internet Protocol Version 6". It is the "next generation" protocol designed by the IETF to replace the current version Internet Protocol, IP Version 4 (IPv4).
Most of today's Internet and our corporate networks use IPv4, which is now more than twenty years old. IPv4 has been remarkably resilient in spite of its age. In the early seventies, when IPv4 was originally developed, the current size of the Internet was beyond imagination. It is remarkable, that this protocol is still able to be the transport for the Internet. But it hits the limits since quite some time. The most obvious limitation is the address space which is short and running out in the near future. We have helped ourselves by using technologies like NAT (Network Address Translation), but this is not a good long term solution. By using the IPv6 address space of 128 bits (compared to 32 bits with IPv4), the limit on addresses has been extended from a theoretical 4 billion to 340 trillion (3.4 x 10^38) - 2^32 compared to 2^128. But limited address space is not the only reason to move toward IPv6. The designers of IPv6 have learned from the many years of using IPv4. They kept all the strengths from IPv4 and added a lot of functionality which will be needed in our future networks. Especially the advanced autoconfiguration features will allow businesses to deploy a great array of new desktop, mobile and embedded network devices in a cost effective, controlled manner. Interesting Mobility Enhancements will provide the foundation for new types of services that are developed these days.
IPv6 also adds many improvements to IPv4 in areas such as security, mobility, quality of service, scalability of the network architecure and routing. IPv6 is therefore very much suited for scalable and converged networks. A number of transition and coexistence mechanisms have been developed and are constantly improved in order to make the transition a smooth one. It is expected that IPv6 will gradually replace IPv4 within the following years, with the two protocols coexisting for many years during a transition period.
Unlike the "old" IPv4 addresses, IPv6 addresses are visualized in hex format and look like this: 2001:08e0:7d83:7d88:4f84:4c74:1d83. or just 2001:08e0::1