IPv4
From Sysadmin
IPv4 is the predominant version of the Internet protocol in use today. IPv4 is approaching exhaustion, in which no new addresses will be available for allocation by the Regional Internet Registries. IPv4 is expected to be superseded by IPv6 within the next few years.
Some subnets within IPv4 are allocated for special purposes. These subnets are detailed in RFC 5735.
