 The shift to IPv6 is expected to take many years, decades, or perhaps longer, to complete, since there were four billion machines with IPv4 when the shift began.The associated standards for IPv4 were published by 1981 as RFCs 791, 792 and 793, and adopted for use.DARPA sponsored or encouraged the development of TCP/IP implementations for many operating systems and then scheduled a migration of all hosts on all of its packet networks to TCP/IP.