Operation Manual

As mentioned, an IPv4 address consists of only 32 bits. Also, quite a few IP addresses
are lost—they cannot be used due to the way in which networks are organized. The
number of addresses available in your subnet is two to the power of the number of bits,
minus two. A subnetwork has, for example, 2, 6, or 14 addresses available. To connect
128 hosts to the Internet, for example, you need a subnetwork with 256 IP addresses,
from which only 254 are usable, because two IP addresses are needed for the structure
of the subnetwork itself: the broadcast and the base network address.
Under the current IPv4 protocol, DHCP or NAT (network address translation) are the
typical mechanisms used to circumvent the potential address shortage. Combined with
the convention to keep private and public address spaces separate, these methods can
certainly mitigate the shortage. The problem with them lies in their conguration, which
is a chore to set up and a burden to maintain. To set up a host in an IPv4 network, you
need a number of address items, such as the host's own IP address, the subnetmask, the
gateway address and maybe a name server address. All these items need to be known
and cannot be derived from somewhere else.
With IPv6, both the address shortage and the complicated conguration should be a
thing of the past. The following sections tell more about the improvements and benets
brought by IPv6 and about the transition from the old protocol to the new one.
21.2.1 Advantages
The most important and most visible improvement brought by the new protocol is the
enormous expansion of the available address space. An IPv6 address is made up of 128
bit values instead of the traditional 32 bits. This provides for as many as several
quadrillion IP addresses.
However, IPv6 addresses are not only different from their predecessors with regard to
their length. They also have a different internal structure that may contain more specic
information about the systems and the networks to which they belong. More details
about this are found in Section 21.2.2, “Address Types and Structure” (page 320).
The following is a list of some other advantages of the new protocol:
Autoconguration
IPv6 makes the network “plug and play” capable, which means that a newly set up
system integrates into the (local) network without any manual conguration. The
new host uses its automatic conguration mechanism to derive its own address
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