Building Nemo, a system to monitor IP routing and traffic paths in real time

Abstract

Efficiently operating and quickly troubleshooting Internet backbones require timely and accurate information about the routing system, their traffic demands, and how they are routed. Unfortunately, the dynamism and complexity of routing protocols, their lack of monitoring features and intricate interaction, together with the volume of routing state make their monitoring network-wide (e.g. across an AS or ISP) hard; while the narrow scope of traffic data provided by existent measurement tools and scalability issues make it difficult to infer the spatial distribution of the traffic. We present the design of a Network Monitoring tool (Nemo) conceived to offer two critical functions: first, monitoring nodes’ routing and forwarding state in nearly real time; second, the ability to derive forwarding paths, which can permit obtaining spatial representations of the traffic when combined with traffic measurement data. We discuss the hardest challenges to overcome to support these functions, how we addressed them, and show preliminary results obtained in two operational networks to illustrate the feasibility and utility of the tool. Nemo was conceived to work with legacy equipment, relying only on standard, widely-supported functions. Nevertheless, we identify downsides of recent monitoring features and suggest simple modifications to router behavior that could greatly ease monitoring the routing system.