--- /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}
+
+\paragraph{IPv4 Link-Local Addressing}
+
+\term{Link-Local Addressing}, also known as \term{Automatic Private IP
+Addressing (APIPA)} or \term{Zeroconf}, uses the IPv4 subnet
+\code{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 \term{IPv6
+Stateless Addressing Autoconfiguration} use an IPv6 address from the subnet
+\code{fe80::/64}. First, an \term{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 \term{Duplicate Address Detection} on the network
+through \term{Neighbor Advertisement} messages and listening for \term{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 \term{Router Solicitation} 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.
+
+% vim: set ft=tex et ts=2 sw=2 :
projects / skm-ma-ws1314.git / blobdiff