Systematic Testing of Multicast Routing Protocols : Analysis of Forward and Backward

| The recent growth of the Internet and its increased het-erogeneity have increased the complexity of network protocol design and testing. In addition, the advent of multipoint (multicast-based) applications has introduced new challenges that are qualitatively diierent in nature than the traditional point-to-point protocols. Multipoint applications typically involve a group of participants simultaneously, and hence are inherently more complex. As more multipoint protocols are coming to life, the need for a systematic method to study and evaluate such protocols is becoming more apparent. Such method aims to expedite the protocol development cycle and improve protocol robustness and performance. In this paper, we present a new methodology for developing systematic and automatic test generation algorithms for multipoint protocols. These algorithms attempt to synthesize network topologies and sequences of events that stress the protocol's correctness or performance. This problem can be viewed as a domain-speciic search problem that suuers from the state space explosion problem. One goal of this work is to circumvent the state space explosion problem utilizing knowledge of network and fault modeling, and multipoint protocols. The two approaches investigated in this study are based on forward and backward search techniques. We use an extended nite state machine (FSM) model of the protocol. The rst algorithm uses forward search to perform reduced reachabil-ity analysis. Using domain-speciic information for multicast routing over LANs, the algorithm complexity is reduced from exponential to polynomial in the number of routers. This approach , however, does not fully automate topology synthesis. The second algorithm, the fault-oriented test generation, uses backward search for topology synthesis and uses backtracking to generate event sequences instead of searching forward from initial states. Using these algorithms, we have conducted studies for cor-rectness of the multicast routing protocol PIM. We propose to extend these algorithms to study end-to-end multipoint protocols using a virtual LAN that represents delays of the underlying multicast distribution tree.