IP Multicast or "push" based technologies are quickly moving into real production systems. UUNET currently offers multicast connections for rent. Several large companies are building multicast-based infrastructures to support multimedia, conferencing, or general multicast-based applications. For large scale and highly available networks, however, the implications of utilizing IP multicast technologies are not well understood. The underlying performance and fault tolerance characteristics of IP Multicast based systems is an area in need of understanding. One way of measuring the performance characteristics of IP Multicast technologies is by building simulation models, and executing series of simulation runs that tabulate the control overhead of IP Multicast protocols. We are currently using a widely used network simulation tool called OPNET that allows one to develop detailed protocol models, execute simulations, gather performance statistics including protocol control overhead and quality-of-service information, for a given topology. Furthermore, within the tools, one can inject switch, router, link, or host failures and measure the fault recovery behavior.