ernet Engineering Task Force, March 1997. 59. Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and Carney, M. Dynamic Host Configuration Protocol for IPv6 (DHCPv6). RFC 3315, Internet Engineering Task Force, July 2003. 60. Rigney, C., Willens, S., Rubens, A., and Simpson, W. Remote Authentication Dial In User Service (RADIUS). RFC 2865, Internet Engineering Task Force, June 2000. 61. Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and Arkko, J. Diameter Base Protocol. RFC 3588, Internet Engineering Task Force, September 2003. 62. Postel, J. User Datagram Protocol. RFC 0768, Internet Engineering Task Force, August 1980. Introduction to IPv6 The 128-bit address space, which provides approximately 3.4 X 10 38 unique addresses, is the main reason for Internet Protocol version 6 (IPv6)'s existence and why it is being deployed. However, the next generation Internet Protocol (IP) is much more than the enormous address space it provides. In this section we will introduce the core features of IPv6, as well as looking at the most relevant additional features, especially from 3rd Generation Partnership Project (3GPP) networks' point of view. These features include, for example, IPv6 packet header structures, address autoconfiguration mechanisms, network and host based IPv6 mobility, different link models, and SO forth. In addition, at the end of the chapter, we provide detailed examples related to IPv6 address configuration, Domain Name System (DNS) use, and Transport Control Protocol (TCP) session establishment. IPv6 is described in over a hundred Internet Engineering Task Force (IETF) RFCs, of which a small minority are essential for an IPv6 enabled node's interoperability with other nodes. Most of the RFCs are optional and need only to be supported by certain kinds of nodes, or in certain deployment scenarios. A node can be a host, a router, or in some cases both. Whether the node is a router or a host is perhaps the biggest single factor that defines what kind of protocol features the node needs. IETF has worke