Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual page 579

30.2.3 Coexistence of IPv4 and IPv6
The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual
process. Both protocols will coexist for some time to come. The coexistence on one
system is guaranteed where there is a dual stack implementation of both protocols. That
still leaves the question of how an IPv6 enabled host should communicate with an IPv4
host and how IPv6 packets should be transported by the current networks, which are
predominantly IPv4 based. The best solutions offer tunneling and compatibility addresses
(see Section 30.2.2, "Address Types and Structure" (page 556)).
IPv6 hosts that are more or less isolated in the (worldwide) IPv4 network can commu-
nicate through tunnels: IPv6 packets are encapsulated as IPv4 packets to move them
across an IPv4 network. Such a connection between two IPv4 hosts is called a tunnel.
To achieve this, packets must include the IPv6 destination address (or the corresponding
prefix) as well as the IPv4 address of the remote host at the receiving end of the tunnel.
A basic tunnel can be configured manually according to an agreement between the
hosts' administrators. This is also called static tunneling.
However, the configuration and maintenance of static tunnels is often too labor-intensive
to use them for daily communication needs. Therefore, IPv6 provides for three different
methods of dynamic tunneling:
6over4
IPv6 packets are automatically encapsulated as IPv4 packets and sent over an IPv4
network capable of multicasting. IPv6 is tricked into seeing the whole network
(Internet) as a huge local area network (LAN). This makes it possible to determine
the receiving end of the IPv4 tunnel automatically. However, this method does not
scale very well and is also hampered by the fact that IP multicasting is far from
widespread on the Internet. Therefore, it only provides a solution for smaller cor-
porate or institutional networks where multicasting can be enabled. The specifica-
tions for this method are laid down in RFC 2529.
6to4
With this method, IPv4 addresses are automatically generated from IPv6 addresses,
enabling isolated IPv6 hosts to communicate over an IPv4 network. However, a
number of problems have been reported regarding the communication between
those isolated IPv6 hosts and the Internet. The method is described in RFC 3056.
Basic Networking 561