Managing large IP networks requires an understanding of the current tra c ows, routing policies, and network con guration. Yet, the state-of-the-art for managing IP networks involves manual con guration of each IP router, and tra c engineering based on limited measurements. The networking industry is sorely lacking in software systems that a large Internet Service Provider (ISP) can use to support tra c measurement and network modeling, the underpinnings of e ective tra c engineering. This

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... describes the AT&T Labs NetScope, a uni ed set of software tools for managing the performance of IP backbone networks. The key idea behind NetScope is to generate global views of the network, on the basis of con guration and usage data associated with the individual network elements. Having created an appropriate global view, we are able to infer and visualize the network-wide implications of local changes in tra c, con guration, and control. Using NetScope, a network provider can experiment w i t h c hanges in network con guration in a simulated environment, rather than the operational network. In addition, the tool provides a sound framework for additional modules for network optimization and performance debugging. We demonstrate the capabilities of the tool through an example tra c-engineering exercise of locating a heavily-loaded link, identifying which tra c demands ow on the link, and changing the con guration of intra-domain routing to reduce the congestion.