Network robustness is something all providers are striving for without being able to know all the aspects it encompasses. A key aspect of network design is the sensitivity of the network to internal failures. In this paper we present an open-source tool implementing the sensitivity model of [1], allowing network operators to study the sensitivity of their network to internal failures. We apply our methodology on the GEANT network, and we show that some of the routers and links of GEANT are sensitive to internal failures. Our results indicate that improvements can be made to the network design so as to reduce the risk of disruptions due to internal failures. Furthermore, we show great consistency between the results of the control plane and the data plane, indicating that applying the analysis on the control plane might be sufficient to provide insight into how to improve the resilience of the network to internal failures.