Transitioning to IPv6 from IPv4 deployments can require a variety of techniques, including
an auto-con?¬?guration function. The transition mechanism you will use depends on the
needs of your network. This section describes the different types of transition mechanisms
for an IPv6 network.
Reasons for Using IPv6
The IPv4 address space provides approximately 4.3 billion addresses. Of that address
space, approximately 3.7 billion addresses are actually assignable; the other addresses are
reserved for special purposes such as multicasting, private address space, loopback testing,
and research. Based on some industry ?¬?gures as of January 1, 2007, about 2.407 billion of
these available addresses are currently assigned to either end users or Internet service
providers (ISPs). That leaves roughly 1.3 billion addresses still available from the IPv4
address space.
An IPv6 address is a 128-bit binary value, which can be displayed as 32 hexadecimal digits,
as shown in the ?¬?gure. It provides 3.4 * 1038 IP addresses. This version of IP addressing
should provide suf?¬?cient addresses for future Internet growth needs. Figure 7-8 illustrates
the differences between the address space for IPv4 and IPv6.
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