IPv6 Address Space Allocation
(Page 3 of 3)
Looking at the IPv6 Address Space Plan As Eight Eighths
An easier way to make sense of this table is to consider the division of the IPv6 address space into eighths. Of these eight groups, one (001) has been reserved for unicast addresses; a second (000) has been used to carve out smaller reserved blocks, and a third (111) has been used for sub-blocks for local and multicast addresses. Five are completely unassigned.
You can see that the IPv6 designers have taken great care to allocate only the portion of these eighths of the address space they felt was needed for each type of address. For example, only a small portion of the part of the address space beginning 111 was used, with most of it left aside. In total, only 71/512ths of the address space is assigned right now, or about 14%. The other 86% is unassigned and kept aside for future use. (Bear in mind that even 1/1024th of the IPv6 address space is gargantuanit represents trillions of trillions of addresses.)
Subsequent topics in this section provide more information on several of these address blocks. Note that the 0000 0000 reserved block is used for several special address types, including the loopback address, the unspecified address and IPv4 address embedding. The 1111 1111 format prefix identifies multicast addresses; this string is FF in hexadecimal, so any address beginning with FF is a multicast address in IPv6.
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