Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 429 — #455
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21
Linux in the Network
The only variable parts of the address are those specifying the site topology
and the public topology, depending on the actual network in which the host
is currently operating.
For a host to go back and forth between different networks, it needs at least
two addresses. One of them, the home address, not only contains the inter-
face ID but also an identifier of the home network to which it normally
belongs (and the corresponding prefix). The home address is a static ad-
dress and, as such, it does not normally change. Still, all packets destined
to the mobile host can be delivered to it, no matter whether it operates in
the home network or somewhere outside. This is made possible by the
completely new features introduced with IPv6, such as stateless autocon-
figuration and neighbor discovery. In addition to its home address, a mobile
host gets one or more additional addresses that belong to the foreign net-
works where it is roaming. These are called care-of addresses. The home
network has a facility that forwards any packets destined to the host when
it is roaming outside. In an IPv6 environment, this task is performed by the
home agent, which takes all packets destined to the home address and re-
lays them through a tunnel. On the other hand, those packets destined to
the care-of address are directly transferred to the mobile host without any
special detours.
21.2.3 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 imple-
mentation 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 21.2.2 on page 425).
IPv6 hosts that are more or less isolated in the (worldwide) IPv4 network
can communicate 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.
429SUSE LINUX Enterprise Server