On the Scalability of BGP: The Role of Topology Growth

The scalability of BGP routing is a major concern for the Internet community. Scalability is an issue in two different aspects: increasing routing table size, and increasing rate of BGP updates. In this paper, we focus on the latter. Our objective is to characterize the churn increase experienced by ASes in different levels of the Internet hierarchy as the network grows. We look at several "what-if" growth scenarios that are either plausible directions in the evolution of the Internet or educational corner cases, and investigate their scalability implications and interaction with different failure types. Our findings explain the dramatically different impact of multihoming and peering on BGP scalability, highlight negative and positive effects of multihoming on churn and reachability, and identify which topological growth scenarios will lead to faster churn increase for different failure types.

I. Introduction

Recently, there is a significant concern among both Internet operators and researchers about the scalability of interdomain routing with BGP. A workshop organized by the Internet Architecture Board concluded that “routing scalability is the most important problem facing the Internet today” [24]. The concern is that we are soon approaching the point where the global routing system, and the core routers in particular, will no longer be able to keep up with routing dynamics. BGP scalability is an issue in two different aspects: increasing routing table size, and increasing rate of BGP updates (churn). Note that, in general, an increase in the routing table size (number of routable prefixes) also increases churn, since the number of networks that can fail or trigger a route change increases. In this paper, we focus on the issue of increasing churn.