A System for the Detection of Limited Visibility in BGP

Abstract

The performance of the global routing system is vital to thousands of entities operating the Autonomous Systems (ASes) which make up the Internet. The Border Gateway Protocol (BGP) is currently responsible for the exchange of reachability information and the selection of paths according to their specified routing policies. BGP thus enables traffic to flow from any point to another connected to the Internet. The manner traffic flows is often influenced by entities in the Internet according to their preferences. The latter are implemented in the form of routing policies by tweaking BGP configurations. Routing policies are usually complex and aim to achieve a myriad goals, including technical, economic and political purposes. Additionally, individual network managers need to permanently adapt to the interdomain routing changes and, by engineering the Internet traffic, optimize the use of their network.

Despite the flexibility offered, the implementation of routing policies is a complicated process in itself, involving fine-tuning operations. Thus, it is an error-prone task and operators might end up with faulty configurations that impact the efficacy of their strate- gies or, more importantly, their revenues. Withal, even when correctly defining legitimate routing policies, unforeseen interactions between ASes have been observed to cause important disruptions that affect the global routing system. The main reason behind this resides in the fact that the actual inter-domain routing is the result of the interplay of many routing policies from ASes across the Internet, possibly bringing about a different outcome than the one expected.

In this thesis, we perform an extensive analysis of the intricacies emerging from the complex netting of routing policies at the interdomain level, in the context of the current operational status of the Internet. Abundant implications on the way traffic flows in the Internet arise from the convolution of routing policies at a global scale, at times resulting in ASes using suboptimal ill-favored paths or in the undetected propagation of configuration errors in the routing system. We argue here that monitoring prefix visibility at the interdomain level can be used to detect cases of faulty configurations or backfired routing policies, which disrupt the functionality of the routing system. We show that the lack of global prefix visibility can offer early warning signs for anomalous events which, despite their impact, often remain hidden from state of the art tools. Additionally, we show that such unintended Internet behavior not only degrades the efficacy of the routing policies implemented by operators, causing their traffic to follow ill-favored paths, but can also point out problems in the global connectivity of prefixes.

We further observe that majority of prefixes suffering from limited visibility at the interdomain level is a set of more-specific prefixes, often used by network operators to fulfill binding traffic engineering needs. One important task achieved through the use of routing policies for traffic engineering is the control and optimization of the routing function in order to allow the ASes to engineer the incoming traffic. The advertisement of more-specific prefixes, also known as prefix deaggregation, provides network operators with a fine-grained method to control the interdomain ingress traffic, given that the longest-prefix match rule over-rides any other routing policy applied to the covering less specific prefixes.

Nevertheless, however efficient, this traffic engineering tool comes with a cost, which is usually externalized to the entire Internet community. Prefix deaggregation is a known reason for the artificial inflation of the BGP routing table, which can further affect the scalability of the global routing system. Looking past the main motivation for deploying deaggregation in the first place, we identify and analyze here the economic impact of this type of strategy. We propose a general Internet model to analyze the effect that advertising more-specific prefixes has on the incoming transit traffic burstiness. We show that deaggregation combined with selective advertisements (further defined as strategic deaggregation) has a traffic stabilization side-effect, which translates into a decrease of the transit traffic bill. Next, we develop a methodology for Internet Service Providers (ISPs) to monitor general occurrences of deaggregation within their customer base. Furthermore, the ISPs can detect selective advertisements of deaggregated prefixes, and thus identify customers which may impact the business of their providers. We apply the proposed methodology on a complete set of data including routing, traffic, topological and billing information provided by an operational ISP and we discuss the obtained results.