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INTERNET PROTOCOL VERSION 6 ADDRESS SPACE
[last updated 1999 Aug 17]
As defined in [RFC2373] the specific type of an IPv6 address is indicated
by the leading bits in the address. The variable-length field comprising
these leading bits is called the Format Prefix (FP).
The current allocation of these prefixes is listed below.
Allocation Prefix Fraction of
(binary) Address Space
----------------------------------- -------- -------------
Reserved 0000 0000 1/256
Unassigned 0000 0001 1/256
Reserved for NSAP Allocation 0000 001 1/128
Reserved for IPX Allocation 0000 010 1/128
Unassigned 0000 011 1/128
Unassigned 0000 1 1/32
Unassigned 0001 1/16
Aggregatable Global Unicast Addresses 001 1/8 [RFC2374]
Unassigned 010 1/8
Unassigned 011 1/8
Unassigned 100 1/8
Unassigned 101 1/8
Unassigned 110 1/8
Unassigned 1110 1/16
Unassigned 1111 0 1/32
Unassigned 1111 10 1/64
Unassigned 1111 110 1/128
Unassigned 1111 1110 0 1/512
Link-Local Unicast Addresses 1111 1110 10 1/1024
Site-Local Unicast Addresses 1111 1110 11 1/1024
Multicast Addresses 1111 1111 1/256
Notes:
(1) The "unspecified address", the "loopback address", and the IPv6
Addresses with Embedded IPv4 Addresses are assigned out
of the 0000 0000 format prefix space and are defined in [RFC2373].
(2) The format prefixes 001 through 111, except for Multicast
Addresses (1111 1111), are all required to have to have 64-bit
interface identifiers in EUI-64 format.
IPv6 Unicast addresses are distinguished from multicast addresses by the
value of the high-order octet of the addresses: a value of 0xFF (binary
11111111) identifies an address as a multicast address; any other value
identifies an address as a unicast address. Anycast addresses are taken
from the unicast address space, and are not syntactically distinguishable
from unicast addresses.
References
----------
[RFC2373] Hinden, R., and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, Nokia, Cisco Systems,
July 1998.
[RFC2374] Hinden, R., M. O'Dell, and S. Deering, "An Aggregatable Global
Unicast Address Format", RFC 2374, Nokia, UUNET, Cisco Systems,
July 1998.
[]
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