Routing changes of the interior gateway protocol (IGP), especially unexpected ones, can significantly affect the connectivity of a network. Although such changes can occur quite frequently in a network, most operators have hardly noticed them because of a lack of effective tools. In this paper, we introduce Rtanaly, a system to (i) detect IGP routing changes in real-time and instantly alert operators of the detected changes, (ii) quantify routing changes over the long term to provide operators with a general view on the routing stability of a network, (iii) estimate the impact of routing changes, and (iv) help operators troubleshoot in response to unexpected changes. Rtanaly has the following features: (i) it supports all three widely deployed IGPs- OSPFv2, OSPFv3, and IS-IS, (ii) it uses a completely passive approach, (iii) it visually displays the measurement results, and(iv) it is accessible through the web. We present the results of measurements that we have performed with Rtanaly as well as some observed pathological behavior to show its effectiveness. We have released the first version of Rtanaly as free software and its distribution is based on a BSD-style license.