Extension headers for IPv6 anycast

Anycast is a new communication paradigm defined in IPv6. Different from unicast and multicast routing, routers on the internetwork deliver an anycast datagram to the nearest available node. By shifting the task of resolving destinations from source node to internetwork, anycasting is highly flexible and cost-effective on routing process and inherently load-balanced and robust on server selection. To achieve these objectives, not only "distance" but also other metrics, such as load balance, reliability, QoS, can and should be taken into account in anycast routing. The IPv6 basic header is designed in a simple and fixed-length format for the purpose of efficient forwarding. Extra data and options needed for packet processing are encoded into extension headers. Such a design makes possible the adding of extension headers for special purposes. In this paper, we define routing extension headers for IPv6 anycasting to enable various types of anycast routing mechanism. Scenarios are also provided to demonstrate how to apply them.