Discovering IPv6 network topology

IPv6 network topology discovery aims at obtaining IPv6 router-level topology so as to mapping the macroscopic topology of an IPv6 network. It is essential for simulating, protocol design, building application and improving network performance. In this paper we introduce the basic method of finding the links between routers firstly. Then, we analyze two challenging problems faced IPv6 network topology discovery, that is, targets selecting and IPv6-in-IPv4 tunnels identifying. Targets selecting affects the probing efficiency, completeness and redundancy of the result. But IPv6 address space is so huge that it's impossible to list every address for probing. To obtain a reasonable targets set, we put forward an efficient dimidiate method to find routers under each IPv6 address prefix. This method lays a stable foundation for the succeeding probing program to improve efficiency, completeness and avoid redundancy. Furthermore, IPv6-in-IPv4 tunnel is a kind of widely used special link during the transition period from IPv4 to IPv6. We propose the method of finding the tunnels based on IPv6 path MTU (Maximum Transfer Unit) discovery mechanism to improve the veracity of the result.