Technology - Internet - Volume 4 - IPv6

This handbook supports technical and management staff in their need to understand the still-developing second generation Internet addressing system and protocols: IPv6. In development since the mid-1990s, IPv6 has not yet been widely adopted, due in large part to compatibility difficulties with IPv4, which is the basis of most Internet communications today.

IPv6’s importance rests on the fact that it is the only alternative to IPv4, at a time when IPv4 address space is becoming harder to obtain, and when major new deployments of IP technology, in developing countries and in handheld mobile devices, are being planned.

We provide a comprehensive introduction to IPv6’s addressing system and to its commonality and differences with IPv4. We offer critical perspectives on some of IPv6's purported benefits, such as its long (128 bit) address system and the yet-to-be completed SHIM6 approach to multihoming.

IPv6 addressing is more complex and flexible than that of IPv4. We discuss the autoconfiguration processes by which an IPv6 host computer develops its own IP addresses, with separate addresses for local and global use. We discuss Unique Local Scope addresses which enable a site to retain a fixed set of addresses, which are not globally routable, no matter which ISP they connect to the Net with.

We discuss IPv6’s extensive support for automated assignment of IP addresses to hosts and routers, which is intended to make it more practical to renumber an entire network from one range of Provider Aggregatable (PA) address space to another, when changing ISPs. Other aspects of IPv6’s address system enable a more standardised and automated approach to addressing than is possible with IPv4, such as the use of a /48 prefix for most end-users, from large companies to residential users, with the capability of running 65,336 LANs, each with an essentially unlimited number of computers.

We discuss the IPv6 extensions to the Domain Name System and the IPv6 packet header, with its system of extension headers for various applications such as Mobile IP and authentication. We provide a detailed description of Mobile IPv6 and some enhancements to it, including NEMO (mobility for entire networks), Fast Handovers and Hierarchical MIPv6 Management (HMIPv6). We also discuss how mobile IPv6 and multicasting might be integrated with cellular mobile systems and how this would compare with alternative arrangements, such as MediaFlo and DVB-H.

We provide a detailed discussion of SHIM6 – the IPv6-specific host-based multihoming protocol. There are several challenges to its successful operation and questions about its usefulness when an entire network is to be multihomed.

The problems IPv4 is experiencing with unconstrained growth in the global Border Gateway Protocol (BGP) routing table are likely to be repeated with IPv6 if and when the latter becomes widely adopted. We discuss attempts to avoid this through the use of address assignment policy and the filtering of BGP advertisements. Now that three RIRs assign Provider Independent /48 prefixes to end-users, we review the difficulty in constraining routing table growth unless a new routing and addressing architecture is developed. We also critique calls for the RIR’s control over IPv6 address assignment to be opened up to include multiple for-profit registration companies.

We review the transition mechanisms for running dual-stack host operating systems with IPv6 connectivity via tunnels over the IPv4 network. There are several approaches to this, including 6to4 and Microsoft’s Teredo. Finally, we consider the countries and application areas where IPv6 is most likely to be adopted, including mobile and IP Multimedia Subsystem (IMS) applications in the USA, Korea and in China.