Comparing IPv4 and IPv6 Addresses
Updated: August 22, 2005
Applies To: Windows Server 2003, Windows Server 2003 with SP1
The size of an IPv6 address is 128 bits, which is four times larger than an IPv4 address. In theory, the 32-bit address space that IPv4 uses provides 4,294,967,296 possible addresses; however, previous and current allocation practices limit the number of public IPv4 addresses to a few hundred million. By contrast, the 128-bit address space that IPv6 uses provides 3.4 x 1038 possible addresses.
The size of the IPv6 address allows for subdividing the address into a hierarchical routing structure that reflects the current topology of the Internet. This structure provides great flexibility for hierarchical addressing and routing, which the IPv4-based Internet lacks.