3.1. The IPv6 Address Space
The 32 bits of the IPv4 address space provide a theoretical maximum of 232 addresses, equal to approximately 4.29 billion addresses. The current world population reaches approximately 6.4 billion people. So even if it were possible to use 100 percent of the IPv4 address space, we would not be able to provide an IP address for everyone on the planet. As a matter of fact, only a small fraction of this address space can be used. In the early days of IP, nobody foresaw the existence of the Internet as we know it today. Therefore, large address blocks were allocated without considerations for global routing and address conservation issues. These address ranges cannot be reclaimed, so consequently there are many unused addresses that are not available for allocation.
If we wanted to provide Internet access to only 20 percent of the world population, the IPv4 address space could never cover the demand. Calculations have shown that this would require around 390 Class A (/8) IPv4 address blocks, but there were only 64 Class A address blocks left in the unallocated IANA pool as of the end of 2005. And the evolution of the Internet and our services shows that in the future, not only are addresses for users and computers needed, but we'll also need more and more addresses for all sorts of devices that need permanent Internet connections, such as cell phones, PDAs, webcams, refrigerators, cars, and many more items. Car manufacturers, as one example, who are designing the networked car of the future, need at least 20 IP addresses per car. These addresses will be used for monitoring and maintenance as well as for access to services such as weather and traffic information. There is a prototype of a Renault car with an integrated Cisco router and a Mobile IPv6 implementation. Most of the big car manufacturers have similar plans and prototypes.
The IPv6 address space uses a 128-bit address, meaning that we have a maximum of 2128 addresses available. Do you want to know what this number looks like? It equals 340,282,366,920,938,463,463,374,607,431,768,211,456, or 6.65 x 1023 addresses per square meter on earth. For all of you who, like me, cannot imagine how much this is, it can be compared to providing multiple IP addresses for every grain of sand on the planet.
The IPv4 address space with the originally defined address classes (A, B, C, D, E) allows for 2,113,389 network IDs. With the introduction of Classless Interdomain Routing (CIDR), this number was slightly extended. Let's compare this with IPv6. The address space with the current prefix for global unicast addresses (binary 001) allows for 245 network IDs with a /48 prefix, or 35,184,372,088,832 networks. Each of these networks can further be divided into 65,536 subnets using the remaining 16 bits of the prefix.