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The world has changed tremendously over the last 10–20 years as a result of the growth
and maturation of the Internet and networking technologies in general. As recently as
1990, a majority of the general public did not know about nor use global networks to
communicate, and when businesses needed to communicate, those communications
mostly flowed over private networks. During the 1990s, the public Internet grew to the
point where people in most parts of the world could connect to the Internet; many companies
connected to the Internet for a variety of applications, with the predominate applications
being email and web. During the first decade of the 21st century, the Internet has
grown further to billions of addressable devices with the majority of people on the planet
having some form of Internet access. With that pervasive access came a wide range of applications
and uses, including voice, video, collaboration, and social networking, with a
generation that has grown up with this easily accessed global network.
The eventual migration to IPv6 will likely be driven by the need for more and more IP addresses.
Practically every mobile phone supports Internet traffic, requiring the use of an
IP address. Most new cars have the capability to acquire and use an IP address, along with
wireless communications, allowing the car dealer to contact the customer when the car’s
diagnostics detect a problem with the car. Some manufacturers have embraced the idea
that all their appliances need to be IP-enabled.
Although the two biggest reasons why networks might migrate from IPv4 to IPv6 are the
need for more addresses and mandates from government organizations, at least IPv6 includes
some attractive features and migration tools. Some of those advantages are
■ Address assignment features: IPv6 supports a couple of methods for dynamic address
assignment, including DHCP and Stateless Autoconfiguration.
■ Built-in support for address renumbering: IPv6 supports the ability to change
the public IPv6 prefix used for all addresses in an Enterprise, using the capability to
advertise the current prefix with a short timeout and the new prefix with a longer
lease life.
■ Built-in support for mobility: IPv6 supports mobility such that IPv6 hosts can
move around the Internetwork and retain their IPv6 address without losing current
application sessions.
■ Provider independent and dependent public address space: ISPs can assign
public IPv6 address ranges (dependent), or companies can register their own public
address space (independent).
■ Aggregation: IPv6’s huge address space makes for much easier aggregation of
blocks of addresses in the Internet, making routing in the Internet more efficient.
■ No need for NAT/PAT: The huge public IPv6 address space removes the need for
NAT/PAT, which avoids some NAT-induced application problems and makes for more
efficient routing.
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Chapter 16 : IP Version 6 Addressing 533
■ IPsec: Unlike IPv4, IPv6 requires that every IPv6 implementation support IPsec.
IPv6 does not require that each device use IPsec, but any device that implements IPv6
must also have the ability to implement IPsec.
■ Header improvements: Although it might seem like a small issue, the IPv6 header
actually improves several things compared to IPv4. In particular, routers do not need
to recalculate a header checksum for every packet, reducing per-packet overhead. Additionally,
the header includes a flow label that allows for easy identification of packets
sent over the same single TCP or UDP connection.
■ No broadcasts: IPv6 does not use Layer 3 broadcast addresses, instead relying on
multicasts to reach multiple hosts with a single packet.
■ Transition tools: As covered in Chapter 18, the IPv6 has many rich tools to help
with the transition from IPv4 to IPv6.
This list includes many legitimate advantages of IPv6 over IPv4, but the core difference,
and the main topic of this chapter, is IPv6 addressing. The first two section of this chapter
examine one particular type of IPv6 addresses, global unicast addresses, which have many
similarities to IPv4 addresses–particularly public IPv4 addresses. The third section broadens
the discussion to include all types of IPv6 addresses, and protocols related to IPv6 address
assignment, default router discovery, and neighbor discovery. The final section looks
at the router configuration commands for IPv6 addressing.