Answers to your Questions

What are the Transition Scenarios?

Three different mechanisms for transition are available - dual-stack, tunneling, and translation. The dual-stack mechanism allows IPv4 and IPv6 to coexist in the same device (host, router, etc.). In the case of a router, it allows this device to communicate with both IPv4- or IPv6-only nodes. In the case of a dual-stack host, both IPv4- and IPv6-only applications can be run. Tunneling enables isolated IPv6 hosts or IPv6 networks to communicate through an IPv4 core network. The IPv6 traffic is tunneled in IPv4 packets in the IPv4 backbone. Finally, the translation mechanism enables an IPv4-only device to communicate with an IPv6-only device by translating the IP layer and/or upper layers from v4 to v6, or vice-versa.

The following mechanisms will be used during transition phases:

During the early phases, isolated IPv6 users will be connected to the IPv6 backbone (called 6BONE) using IPv6 tunneling over an IPv4 core network. Consequently, an ISP will need a scalable method for automatically setting up tunnels over an IPv4 core network. One proposed method is to tunnel IPv6 traffic via MPLS by adding a shim header to the IPv6 packet. Another method is to use a dedicated data link layer protocol (such as ATM or frame relay) to carry IPv6 traffic in the IPv4 core. With these methods, dual-stack routers are required only at the edge of the IPv6 and IPv4 networks. Routers in the core do not need to upgrade.

In later phases, the ISP will either upgrade all routers in the core network with dual-stack capabilities or build a new IPv6 backbone.