Studying interdomain routing over long timescales

Abstract

The dynamics of interdomain routing have traditionally been studied through the analysis of BGP update traffic. However, such studies tend to focus on the volume of BGP updates rather than their effects, and tend to be local rather than global in scope. Studying the global state of the Internet routing system over time requires the development of new methods, which we do in this paper. We define a new metric, MRSD, that allows us to measure the similarity between two prefixes with respect to the state of the global routing system. Applying this metric over time yields a measure of how the set of total paths to each prefix varies at a given timescale. We implement this analysis method in a MapReduce framework and apply it to a dataset of more than 1TB, collected daily over 3 distinct years and monthly over 8 years. We show that this analysis method can uncover interesting aspects of how Internet routing has changed over time. We show that on any given day, approximately 1% of the next-hop decisions made in the Internet change, and this property has been remarkably constant over time; the corresponding amount of change in one month is 10% and in two years is 50%. Digging deeper, we can decompose next-hop decision changes into two classes: churn, and structural (persistent) change. We show that structural change shows a strong 7-day periodicity and that it represents approximately 2/3 of the total amount of changes.