\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}
+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. Letting the user choose and configure IP addresses manually is a cumbersome
+when it comes to several devices. Deploying a central server for assigning IP
+addresses automatically from a pre-configured address pool is possible (e.~g. by
+using DHCP~\cite{rfc2131}), however, there is also the alternative
+to use a distributed protocol which enables the devices on a network to choose
+addresses in accordance with each other, so no IP address is used twice.
+
+In respect to the Internet of Things, this decentralized approach has the
+advantage that devices can easily be used in different deployments, even where
+central infrastructures do not exist, and it also allows them to change their
+addresses dynamically in order to react 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 specified in the IPv6 protocol.
\paragraph{IPv4 Link-Local Addressing}
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.
+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.
+Stateless Address Auto\-configuration} use an IPv6 address from the subnet
+\code{fe80::/64}. First, a 64-bit \term{interface identifier} is generated,
+which can be random, or based on the interface's MAC address. Most likely, this
+interface identifier is unique in the network, so a unique IPv6 address is
+obtained by combining the subnet prefix and the interface identifier.
+Nonetheless, to ensure that no other device uses the generated IPv6 address, the
+device performs \term{Duplicate Address Detection} on the network by
+broadcasting its generated address with \term{Neighbor Advertisement} messages
+and listening for \term{Neighbor Solicitation} messages. If such a message is
+received from another hosts, the generated address cannot be used by the device
+and must be discarded, and the address generation process is repeated until a
+unique address has been found.
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
+Autoconfiguration can also be used with a central server. In this case, the
+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.
projects / skm-ma-ws1314.git / blobdiff