Operation Manual
::1 (loopback)
The address of the loopback device.
IPv4 Compatible Addresses
The IPv6 address is formed by the IPv4 address and a prex consisting of 96 zero
bits. This type of compatibility address is used for tunneling (see Section 13.2.3,
“Coexistence of IPv4 and IPv6” (page 237)) to allow IPv4 and IPv6 hosts to com-
municate with others operating in a pure IPv4 environment.
IPv4 Addresses Mapped to IPv6
This type of address species a pure IPv4 address in IPv6 notation.
Local Addresses
There are two address types for local use:
link-local
This type of address can only be used in the local subnetwork. Packets with a
source or target address of this type should not be routed to the Internet or
other subnetworks. These addresses contain a special prex (fe80::/10)
and the interface ID of the network card, with the middle part consisting of
zero bytes. Addresses of this type are used during automatic conguration to
communicate with other hosts belonging to the same subnetwork.
site-local
Packets with this type of address may be routed to other subnetworks, but not
to the wider Internet—they must remain inside the organization's own network.
Such addresses are used for intranets and are an equivalent of the private address
space dened by IPv4. They contain a special prex (fec0::/10), the inter-
face ID, and a 16 bit eld specifying the subnetwork ID. Again, the rest is
lled with zero bytes.
As a completely new feature introduced with IPv6, each network interface normally
gets several IP addresses, with the advantage that several networks can be accessed
through the same interface. One of these networks can be congured completely auto-
matically using the MAC and a known prex with the result that all hosts on the local
network can be reached as soon as IPv6 is enabled (using the link-local address). With
the MAC forming part of it, any IP address used in the world is unique. The only variable
parts of the address are those specifying the site topology and the public topology, de-
pending on the actual network in which the host is currently operating.
236 Reference