Computer Science Department
School of Computer Science, Carnegie Mellon University


On Static Reachability Analysis of IP Networks

Geoffrey G. Xie*, Jibin Zhan, David A. Maltz, Hui Zhang
Albert Greenberg**, Gisli Hjalmtysson**+, Jennifer Rexford**

June 2004


Keywords: Routing protocols, routing design, routing analysis

The primary purpose of a network is to provide reachability between applications running on end hosts. In this paper, we describe how to compute the reachability a network provides from a snapshot of the configuration state from each of the routers. Our primary contribution is the precise definition of the potential reachability of a network and a substantial simplication of the problem through a unified modeling of packet filters and routing protocols. In the end, we reduce a complex, important practical problem to computing the transitive closure to set union and intersection operations on reachability set representations. We then extend our algorithm to model the influence of packet transformations (e.g., by NATs or ToS remapping) along the path. Our technique for static analysis of network reachability is valuable for verifying the intent of the network designer, troubleshooting reachability problems, and performing "what-if" analysis of failure scenarios.

37 pages

*Visiting Researcher, Naval Postgraduate School **AT&T Labs-Research
+Revkaivik University

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