X-Git-Url: http://git.rohieb.name/skm-ma-ws1314.git/blobdiff_plain/a1c81dce7c7d4e3a0e6e1f446eaeb893845fd680..c1cb1bb55ce5e742d4a17ed21c384a712d2dce28:/sec-address-allocation.tex

diff --git a/sec-address-allocation.tex b/sec-address-allocation.tex
index 4198074..0ca0764 100644
--- a/sec-address-allocation.tex
+++ b/sec-address-allocation.tex
@@ -1,39 +1,24 @@
 \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}
 
@@ -46,27 +31,28 @@ 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.
+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.
 
