其实，IPv5是有的，只不过仅限于实验和过渡，并不会推向市场。请看：
IPv4: Currently used by most network devices. However, with more and more computers accessing the internet, IPv4 IPs are running out quickly. Just like in a city, addresses have to be created for new neighborhoods but, if your neighborhood gets too large, you will have to come up with an entire new pool of addresses. IPv4 is limited to 4,294,967,296 IPs.
IPv5: This is an experimental protocol for UNIX based systems. In keeping with standard UNIX (a computer Operating System) release conventions, all odd-numbered versions are considered experimental. It was never intended to be used by the general public.
IPv6: The replacement for the aging IPv4. The estimated number of unique IPs for IPv6 is 340,282,366,920,938,463,463,374,607,431,768,211,456 (or 2^128).
来自: http://www.whatismyip.com/#ixzz1aR9kgprq
