The current 32-bit IP addressing scheme used on TCP/IP networks worldwide. Because the number of hosts connecting to the Internet has skyrocketed in recent years, unique IP addresses are gradually running out.
A new scheme called IPv6 has been proposed and is currently under review by the Internet community. However, with most corporate networks now hiding their networks behind firewalls, the pressure to move to IPv6 has lessened because companies can choose any network ID they want for their private network.
The only assigned IP addresses they require from their Internet service provider (ISP) are for the public interfaces on their firewall machines. At this point, IPv4 seems to be firmly entrenched in the networking world for at least the next few years.