IPv4 space is becoming scarcer by the day. By 2005, some estimates place the number of worldwide Internet users at over one billion. Given the fact that many of those users will have a cellular phone, a home computer, and possibly a computer at work, the available IP address space becomes critically tight. China has recently requested IP addresses for each of their students, for a total of nearly 300 million addresses. Requests such as these, which cannot be filled, demonstrate this shortage. When IANA initially began allotting address space, the Internet was a small and little- known research network. There was very little demand for addresses and class A address space was freely allocated. However, as the size and importance of the Internet started to grow, the number of available addresses diminished, making obtaining a new IP difficult and much more expensive. NAT and CIDR are two separate responses to this scarcity. NAT is an individual solution allowing one site to funnel its users through a single IP address. CIDR allows for a more efficient division of network address block. Both solutions, however, have limitations.
With new electronic devices such as PDAs and cellular phones, which all need IP addresses of their own, the NAT address blocks suddenly do not seem quite as large.
Researchers, realizing the potential IP shortage, have redesigned the IPv4 protocol so that it supports 128-bits worth of address space. The selected 128-bit address space provides 340 trillion possible addresses, an exponential increase that we hope will provide adequate addressing into the near (and far) future. This is, in fact, enough addresses to provide every person on Earth with one billion addresses.
Not only does IPv6 solve some of the address space logistics, it also addresses some configuration and security issues. In this section, we'll take a look at the current solutions available with Linux and IPv6.