Mobilité en ipv6

Introduction

IP version 6 (IPv6) is being designed within the IETF as a replacement for the current version of the IP protocol used in the Internet (IPv4). We have designed protocol enhancements for IPv6, known as Mobile IPv6, that allow transparent routing of IPv6 packets to mobile nodes, taking advantage of the opportunities made possible by the design of a new version of IP. In Mobile IPv6, each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While away from its home IP subnet, a mobile node is also associated with a care-of address, which indicates the mobile node's current location. Mobile IPv6 enables any IPv6 node to learn and cache the care-of address associated with a mobile node's home address, and then to send packets destined for the mobile node directly to it at this care-of address using an IPv6 Routing header.

The problem of mobility in IPv6 can be divided in three sub problems distinct:
∙ to be able to communicate;
∙to be reachable;
∙ keep current communications while changing the network;
The first problem is solved by the auto configuration mechanism IPv6, indeed, as soon as the terminal has managed to build an address Global IPv6, it is able to communicate with any other station on the Internet.
Mobile IPv6 (MIPv6) modifies very little these mechanisms. It only requires new configuration allowing to speed up the process because the delay acquisition of a routable global address is critical in situations mobility.

The second problem is solved for device that have a fixed IP with the DNS which establishes the relationship between a logical name and an IP address (Naming). In context of mobility, the frequency of assigning a new address is incompatible with the distributed DNS update. Other mechanisms have been proposed like DDNS (Dynamic Domain Name System).

The third problem is more difficult to solve. It originates from the duality of functions of an IPv6 address. It identifies on the Internet one terminal, or to be more precise one network interface of a terminal. It permits also to locate a node in the topology of the Internet. So every time the node moves, it must change address for the new address corresponds to its new location (location function). Unfortunately its identification also changes which causes problems to upper layers, so to resolve this issue many various possible optimizations have been considered and made the Mobile IPv6 standardization long and laborious, the RFCs being published only in June 2004. The mobility management in IPv6 is now defined in the RFC 6275 for its functional aspects

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1. THE MOBILE IN HER HOME NETWORK

When the mobile is attached to the home network, it has its mother address and communicates normally using its HoA (home of address) as the source address. The packets intended for it include the home address as an address destination and are routed according to the prefix of the home network. The home agent is inactive. There is no additional security problem induced by management mobility because the mobile communicates in the same way as any other IPv6 node on the Internet.
The home network is not necessarily a network on which the mobile can be attached in, its main role is to host the home agent and the home addresses
the mobiles he manages. There is however a strong administrative relationship between the mobile and its home network.

1. THE MOBILE IN A FOREIGN NETWORK

As soon as a node detects that it is now in a new network, it uses to ICMPv6 that self-configures a new IP address. This new address is the care-of address of the node. It then sends to its Home Agent a BU (binding update) containing this new address for allow it to associate with the original address of the node. Home Agent responds with a Back (Binding Acknowledgement).

All new messages used in mobile IPv6 are defined as IPv6 destination options (Ipv6 destination options). These options contain additional information that the destination will have to deal.

1. TRIANGULAR ROUTING

When the mobile is attached to a foreign network, it has, in addition to its address, one or more routable temporary addresses acquired by the self-configuration mechanisms with or without states. One of these addresses is chosen as the primary temporary address and sent to the home agent to create an association between HoA and this primary CoA.
The parent agent maintains a "table of associations" containing the associations of all the mobiles that it manages and which are visiting a foreign network (see figure1). Thanks to
this information he can forward packets to the HoA from a correspond node to the primary CoA. It encapsulates for that the packets in using IPv6's IP-IP header extension. The packets thus tunneled are
protected by IPsec. The IP packet retransmitted to the mobile has as its source address that of the
HA and as destination address the primary CoA of the mobile. The packet reaches the
foreign network since the primary CoA has as prefix one of those of the network foreign. The mobile receives this packet and discovers the IP header extension in IP. It removes the outer header and puts the packet back to the upper layers as if the mobile had received the packet in its home network.

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