Protocol IPv6 puts new challenges for network administrators in the context of user identification. Unlike IPv4, an IPv6 address no longer uniquely identifies a user or PC. IPv6 address can be randomly generated and keeps changing in time. The presentation describes the system developed at the Brno University of Technology, that gathers data from multiple sources (netflow probes, routers, switches, authentication servers) and puts them together. Based on that data the user the flow data are extended by extra information that allows user tracking in a IPv6 enviroment.