The growth of IP address use is exponential.
Predictions indicated that the IPv4 address pool could be exhausted as early as 1994.
So, in July 1991, the Internet Engineering Task Force (IETF) began researching a replacement for IPv4.
That replacement is IPv6.
The Internet Assigned Numbers Authority (IANA) free pool of IPv4 addresses reached 0% in February 2011, according to the American Registry for Internet Numbers (ARIN).
While IPv4 addresses may remain available for some time within reserved pools, no further IPv4 addresses are available for reservation.
Although IPv6 is designed to replace IPv4, IPv6 is not backward-compatible and IPv4 and IPv6 need to coexist within your network during and after the transition to IPv6.