--- /dev/null
+\subsection{Address allocation}
+Considering the TCP/IP protocol suite, in order to be able to communicate on the
+IP layer, a device needs to configure one of its network interfaces with
+an IP address that can be reached from the network that the device wants to connect
+to. There are several ways of achieving this:
+
+\begin{itemize}
+ \item The IP address is pre-selected by a human and stored in the device
+ configuration. This process is cumbersome when more than one device needs to
+ be configured, and humans have to remember which addresses are configured on
+ which device, and which addresses are still free to use on additional
+ devices.
+
+ \item Deploying a central server that assigns network addresses
+ to the devices in the network, which in order query the server (for example
+ via broadcast or on a lower layer) for a unique address before they use the
+ IP layer for the first time. This technique supersedes the dependency of
+ human memory for mapping IP addresses to devices, and can easily be combined
+ with additional central configuration management, like the automatic
+ assignment of a static gateway, or a DNS resolver.\\
+ The DHCP protocol is one example of central IP address management.
+
+ \item A third alternative is the use of a distributed protocol which enables
+ the devices on the network to choose addresses in accordance with other
+ devices on the same network, so no IP address is used more than once. In
+ respect to the Internet of Things, this approach has the advantage that
+ those devices can easily be used in different scenarios without needing
+ central deployment at all, and also allowing them to change their addresses
+ dynamically, therefore easily reacting to changes in the network. \\
+ There are two major protocols which are used for dynamic configuration of IP
+ addresses. In the IPv4 world, Link-Local Addressing~\cite{rfc3927} is often
+ used, and in IPv6 networks, Stateless Address
+ Autoconfiguration~\cite{rfc4862} is a fundamental feature built into every
+ device.
+
+\end{itemize}
+
+\todo
+
+\paragraph{IPv4 Link-Local Addressing}
+
+Link-Local Addressing uses the IPv4 subnet 169.254.0.0/16 for addressing. Every
+device first chooses a random address from that address space. Then it checks if
+the chosen address is used by any other device on the network by probing the
+chosen address, which is usually done using the ARP protocol. If the probing
+process results that the address is not used on the network (e.~g. no device
+returned an ARP response during a random time interval), the device claims its
+chosen address and uses it for communication on the IPv4 layer. If the chosen
+address is already used, the device continues the process, subsequently choosing
+a new random address and trying to claim it, until a free address has been
+found.
+
+\paragraph{IPv6 Stateless Address Autoconfiguration}
+
+Similar to IPv4 Link-Local Addressing, devices configured with IPv6 Stateless
+Addressing Autoconfiguration use an IPv6 address from the subnet fe80::/64.
+Then, an \emph{interface identifier} is generated using the interface's MAC
+address. Since MAC addresses must be unique in the network, a unique IPv6
+address is obtained by combining the subnet prefix and the interface identifier.
+To ensure that no other device exists with this generated IPv6 address, the
+device performs \emph{Duplicate Address Detection} on the network through
+\emph{Neighbor Advertisement} messages and listening for \emph{Neighbor
+Solicitation} messages. If such messages are received from other hosts, the
+configured address cannot be used by the device and must be discarded.
+Therefore, in order to use IPv6 effectively, it must be guarranteed that MAC
+addresses are unique on the network.
+
+In contrast to IPv4 Link-Local Addressing, IPv6 Stateless Address
+Autoconfiguration can also be used with a central server. In this case, a
+central server broadcasts \emph{Router Advertisement} messages on the network which
+contain a global network prefix. The hosts on the network can then use that
+prefix instead to configure a global IPv6 address.
+
+addressing
+
+automatic address configuration via Zeroconf/APIPA (IPv4, \cite{rfc3927}) or
+IPv6 stateless auto-configuration \cite{rfc4862}
+
+\pages{1}
+
+% vim: set ft=tex et ts=2 sw=2 :
projects / skm-ma-ws1314.git / blobdiff