Systematic testing of multicast routing protocols: analysis of forward and backward search techniques

The recent growth of the Internet and its increased het erogeneity have increased the complexity of network proto col design and testing In addition the advent of multipoint multicast based applications has introduced new challenges that are qualitatively di erent in nature than the traditional point to point protocols Multipoint applications typically in volve 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 develop ing 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 speci c search problem that su ers from the state space explosion problem One goal of this work is to circumvent the state space explosion problem utilizing knowl edge of network and fault modeling and multipoint protocols The two approaches investigated in this study are based on for ward 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 speci c information for multicast routing over LANs the algorithm complexity is reduced from exponential to polynomial in the number of routers This ap proach 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 pro tocols using a virtual LAN that represents delays of the un derlying multicast distribution tree