logs in to a foreign service as soon as it enters the corresponding area, so you can
be reached under the same number everywhere and are able to place an outgoing
call just like in your home area.
Secure Communication
With IPv4, network security is an add-on function. IPv6 includes IPsec as one of
its core features, allowing systems to communicate over a secure tunnel to avoid
eavesdropping by outsiders on the Internet.
Backward Compatibility
Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6
at one time. Therefore, it is crucial that both protocols are able to coexist not only
on the Internet, but also on one system. This is ensured by compatible addresses
(IPv4 addresses can easily be translated into IPv6 addresses) and through the use
of a number of tunnels. See Section 13.2.3, “Coexistence of IPv4 and
IPv6” (page 237). Also, systems can rely on a dual stack IP technique to support
both protocols at the same time, meaning that they have two network stacks that
are completely separate, such that there is no interference between the two protocol
versions.
Custom Tailored Services through Multicasting
With IPv4, some services, such as SMB, need to broadcast their packets to all hosts
in the local network. IPv6 allows a much more ne-grained approach by enabling
servers to address hosts through multicasting—by addressing a number of hosts as
parts of a group (which is different from addressing all hosts through broadcasting
or each host individually through unicasting). Which hosts are addressed as a group
may depend on the concrete application. There are some predened groups to ad-
dress all name servers (the all name servers multicast group), for example, or all
routers (the all routers multicast group).
13.2.2 Address Types and Structure
As mentioned, the current IP protocol is lacking in two important aspects: there is an
increasing shortage of IP addresses and conguring the network and maintaining the
routing tables is becoming a more complex and burdensome task. IPv6 solves the rst
problem by expanding the address space to 128 bits. The second one is countered by
introducing a hierarchical address structure, combined with sophisticated techniques
to allocate network addresses, as well as multihoming (the ability to assign several ad-
dresses to one device, giving access to several networks).
232 Reference
