Section 3.5. Global Routing Prefixes

3.5. Global Routing Prefixes

Table 3-2 outlines the current assignment of reserved prefixes and special addresses, such as link-local addresses or multicast addresses. The major part of the address space (over 80 percent) is unassigned, which leaves room for future assignments.

Table 3-2. List of assigned prefixes


Prefix binary

Prefix hex

Fraction of address space


0000 0000




0000 001



Global unicast




Link-local unicast

1111 1110 10



Reserved (formely Site-local unicast)

1111 1110 11

FEC0::/10* * deprecated


Local IPv6 address

1111 110



Private administration

1111 1101




1111 1111



All address ranges not listed in Table 3-2 are currently reserved or unassigned. The Internet Assigned Numbers Authority (IANA) currently assigns only out of the binary range starting with 001.

The updated list of address allocations can be found at:

Some special addresses are assigned out of the reserved address space with the binary prefix 0000 0000. These include the unspecified address , the loopback address , and IPv6 addresses with embedded IPv4 addresses, which I discuss in detail later in this chapter.

Unicast addresses can be distinguished from multicast addresses by their prefixes. Globally unique unicast addresses have a high-order byte starting with 001. An IPv6 address with a high-order byte of 1111 1111 (FF in hex) is always a multicast address. For more information about multicast addresses, refer to the "Multicast Address" section later in this chapter.

Anycast addresses are taken from the unicast address space, so they can't be identified as anycast just by looking at the prefix. If you assign a unicast address to multiple interfaces, thereby making it an anycast address, you have to configure the interfaces so they all know that this address is an anycast address. For more information about anycast addresses, refer to the "Anycast Address" section later in this chapter.

IPv6 Essentials
IPv6 Essentials
ISBN: 0596100582
EAN: 2147483647
Year: 2004
Pages: 156
Authors: Silvia Hagen

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