<P> IPv4 address exhaustion is the depletion of the pool of unallocated IPv4 addresses . Because there are fewer than 4.3 billion addresses available, depletion has been anticipated since the late 1980s, when the Internet started to experience dramatic growth . This depletion is one of the reasons for the development and deployment of its successor protocol, IPv6 . Currently IPv4 and IPv6 coexist in the Internet . </P> <P> The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIR) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers . The main market forces that accelerated IPv4 address depletion included the rapidly growing number of Internet users, always - on devices, and mobile devices . </P>

How have we not run out of ip addresses