2.6.9 IPv6 Command
Brief Introduction to IPv6 Addressing
IPv6 addresses are 128 bits long and number about 3.4×1038. IPv6 addresses are written in eight
groups of four hexadecimal digits separated by colons, such as
2001:0db8:85a3:0000:0000:8a2e:0370:7334
IPv6 unicast addresses other than those that start with binary 000 are logically divided into two
parts: a 64-bit network prefix and a 64-bit interface identifier.
Stateless Autoconfiguration
IPv6 lets any host generate its own IP address and check if it's unique in the scope where it will be
used. IPv6 addresses consist of two parts. The leftmost 64 bits are the subnet prefix to which the
host is connected, and the rightmost 64 bits are the identifier of the host's interface on the subnet.
This means that the identifier need only be unique on the subnet to which the host is connected,
which makes it much easier for the host to check for uniqueness on its own.
Link local address
The first step a host takes on startup or initialization is to form a link-local address from its MAC
address and the link-local prefix FE80::/10. This is done by putting the prefix into the leftmost bits
and the MAC address (in EUI-64 format) into the rightmost bits, and if there are any bits left in
between, those are set to zero.
Global address
This is done in the same fashion as the link-local address, but instead of the link-local prefix FE80::
it will use the prefix supplied by the router and put it together with its identifier (which by default is
the MAC address in EUI-64 format).
Some IPv6 addresses are reserved for special purposes, such as loopback, 6to4 tunneling, and
Teredo tunneling, as outlined in RFC 5156. Also, some address ranges are considered special,
such as link-local addresses for use on the local link only, Unique Local addresses (ULA), as
described in RFC 4193, and solicited-node multicast addresses used in the Neighbor Discovery
Protocol.
DHCPv6
IPv6 hosts may automatically generate IP addresses internally using stateless address
autoconfiguration, or they may be assigned configuration data with DHCPv6.
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