Hot-potato routing is a mechanism employed when there are multiple (equally good) interdomain routes available for a given destination. In this scenario, the Border Gateway Protocol (BGP) selects the interdomain route associated with the closest egress point based upon intradomain path costs. Consequently, intradomain routing changes can impact interdomain routing and cause abrupt swings of external routes, which we call hot-potato disruptions. Recent work has shown that hot-potato disruptions

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... an have a substantial impact on large ISP backbones and thereby jeopardize the network robustness. As a result, there is a need for guidelines and tools to assist in the design of networks that minimize hot-potato disruptions. However, developing these tools is challenging due to the complex and subtle nature of the interactions between exterior and interior routing. In this paper, we address these challenges using an analytic model of hot-potato routing that incorporates metrics to evaluate network sensitivity to hot-potato disruptions. We then present a methodology for computing these metrics using measurements of real ISP networks. We demonstrate the utility of our model by analyzing the sensitivity of a large AS in a tier 1 ISP network. Network robustness, sensitivity analysis, hot-potato routing, BGP, IGP, OSPF trix is a function of the routes sent to an AS and the locally implemented routing policies. The routing matrix stores the set of egress points that are best according to BGP and that have equal IGP distances from the node. Changes in both IGP and BGP may affect a network routing matrix. We express this dependence informally in the following relation, where © represents the combination of information from the two protocols: