Modeling the Routing of an Autonomous System with C-BGP

Bruno Quoitin and Steve Uhlig

Today, the complexity of ISPs' networks make it difficult to investigate the implications of internal or external changes on the distribution of the traffic across their network. In this paper, we explain the complexity of building models of large ISPs' networks. We describe the various aspects important to understand the routing inside an AS. We present an open-source routing solver, called C-BGP, that eases the investigation of changes in the routing or the topology of large networks. We illustrate how to build a model of an ISP on real transit network and apply the model on two ``what-if''scenarios. The first scenario studies the impact of changes in the Internet connectivity of the transit network. The second investigates the impact of failures in its internal topology.
Published in IEEE Network, November 2005.

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