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Home » Volume 01 Issue 08 September 2009 » Software Dev
Mobility for IPv6

            Asela Bandara

Introduction

The rapid growth in the number of wireless and handheld devices is putting a strain on the current IP protocol, version 4, which is not able to keep pace with the increasing demands brought about by the evolving Internet. Internet Protocol Version 4 (IPv4) has been the dominant Internet Protocol (IP) technology for twenty years, resilient through the exponential growth in the Internet and rapid changes in its related technologies over the decades. But the limitations of (IPv4) have been causing increasing concern to technology around the globe, causing a new version of the Internet Protocol, called IPv6, to be designed.

                    Figure1: IPv6 Datagram                                          Figure2: IPv4 Datagram     

The biggest problem with the Internet Protocol as it exists today is that we are rapidly reaching a point where available network address space is running out. IPv4 allows for about 2^32 or 4,294,967,296 addresses which, mainly due to initial misallocation, has already been completely allocated and therefore, leaves no room for growth. The new version of IP, IPv6, offers a more permanent solution, allowing for about 2^128 or 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses.

This seemingly limitless number of addresses is exactly what is needed to allow growth for the many new Internet-ready devices that are forecasted to become globally prevalent.




Figure3: IPv6 Architecture: Core protocols in relation to the OSI model, the TCP/IP protocol architecture, and the other protocols in the TCP/IP suite.

As per the requirements arose in Mobile computing, the IPv4 was designed with the mobility support to take the mobile devices’ integrated to the global network of computers. But it was not initially designed with support for mobile users because mobility was not an issue when the Internet began. Mobility was later added as extensions to the IPv4 protocol. However, the IPv6 implementation of mobility was designed into the protocol from the ground up, providing better support and integration with the underlying mechanisms.


Main feature of IPv6

The following are the features of the IPv6 protocol:

  1. New header format - IPv4 headers and IPv6 headers are not interoperable and the IPv6 protocol is not backward compatible with the IPv4 protocol.


Figure4: Structure of an IPv6 Packet




  1. Large address space - IPv6 has 128-bit (16-byte) source and destination addresses.

  2. Efficient and hierarchical addressing and routing infrastructure - On the IPv6 Internet, backbone routers have much smaller routing tables.

  3. Stateless and stateful address configuration - IPv6 supports both stateful address configuration

  4. Built-in security - Support for IPSec is an IPv6 protocol suite requirement.

  5. Better support for quality of service (QoS) - New fields in the IPv6 header define how traffic is handled and identified.

  6. New protocol for neighboring node interaction - The Neighbor Discovery protocol for IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manage the interaction of neighboring nodes (that is, nodes on the same link) (ARP, ICMPv4 Router Discovery).

  7. Extensibility- IPv6 can be extended for new features by adding extension headers after the IPv6 header. Unlike the IPv4 header, which can only support 40 bytes of options, the size of IPv6 extension headers is only constrained by the size of the IPv6 packet.


Mobile IPv6 over Mobile IPv4

  • Route Optimization is built as a fundamental part of Mobile IPv6 unlike Mobile IPv4.

  • Foreign Agents are not needed in Mobile IPv6. The enhanced features of IPv6 like Neighbor Discovery and Address Auto configuration enable mobile nodes to function in any location without the services of any special router in that location.

  • In Mobile IPv4, when a mobile node communicates with a correspondent node, it puts its home address as the source address of the packet. Thus “ingress filtering routers " used to filter out the packets as the source address of the packet is different from the network from which the packet originated. This problem is tackled in Mobile IPv6 by putting the care-of address as the source address and having a Home Address Destination option, allowing the use of the care-of address to be transparent over the IP layer

Mobile IPv6 Operation

·        Home Agent Registration

  •  An MN performs address auto configuration (stateful or stateless) to get its care-of address

  • The MN registers its care-of address with its home agent on the home link

  • Use “Binding Update” Destination Option

  • The HA uses proxy Neighbor Discovery and also replies to Neighbor Solicitations on behalf of the MN