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[skm-ma-ws1314.git] / sec-address-allocation.tex

diff --git a/sec-address-allocation.tex b/sec-address-allocation.tex
index 4198074..0ca0764 100644 (file)
--- a/sec-address-allocation.tex
+++ b/sec-address-allocation.tex
@@ -1,39 +1,24 @@
 \subsection{Address allocation}
 \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}
 
 
 \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
 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
 
 \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
 
 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.
 
 which contain a global network prefix. The hosts on the network can then use
 that prefix instead to configure a global IPv6 address.