et Engineering Task Force, December 2012. Work in progress. 192. Giobbi, R. Bypassing firewalls with IPv6 tunnels. html, CERT, April 2009. 193. Davies, E. and Mohacsi, J. Recommendations for Filtering ICMPv6 Messages in Firewalls. RFC 4890, Internet Engineering Task Force, May 2007. 194. Gont, F. Processing of IPv6 "atomic" fragments. Internet-Draft draft-ietf-6man-ipv6-atomic-fragments-03, Internet Engineering Task Force, December 2012. Work in progress. 195. Gont, F. Security Implications of Predictable Fragment Identification Values. Internet-Draft draft-gont- 6man-predictable-fragment-id-03, Internet Engineering Task Force, January 2013. Work in progress. IPv6 Transition Mechanisms for 3GPP Networks This chapter starts with the motivation for the Internet Protocol version 6 (IPv6) transition and then follows with a high level overview of the technical solution approaches and their benefits and drawbacks. With the motivation and set of solution approaches described, we will list the detailed toolbox and scenarios for the IPv6 transition for 3rd Generation Partnership Project (3GPP) networks. We conclude the chapter by listing the impacts that IPv6 transition has on the 3GPP architecture and how application writers, phone vendors, and network operators can plan the transition. Motivation for Transition Mechanisms The main motivation to move to IPv6 is the Internet Protocol version 4 (IPv4) address shortage and the implications it causes: need for address translation, overlapping private address spaces, and SO forth. All of those result in increased costs for operating IPv4 networks, and they hinder innovation. The IPv6 removes the address shortage, and the side-effects it has caused, thus promising operational cost savings in the long run. All the other reasons for deploying IPv6 are secondary, and often also result from the increased address space. A large set of tools and techniques have had to be developed to make the long transition from the IPv4-only world to the world dominated by IPv6 smooth and seamless