Managing the Complexity of Modern Enterprise Networks

Operator interviews and anecdotal evidence suggest that an operator's ability to manage a network decreases as the network becomes more complex. Today, there is no way to quantify how complex a network's design is, nor how complexity may impact network management activities. In this talk, I will present a suite of "complexity models" that describe the routing design and configuration of a network in a succinct fashion, abstracting away details of the underlying configuration languages. Our models, and the complexity metrics arising from them, capture the difficulty of configuring control and data plane behaviors on routers. They also measure the inherent complexity of the reachability constraints that a network implements via its routing design. Our models simplify network design and management by facilitating comparison between alternative designs for a network.

We tested our models on seven networks, including four universities and three enterprises. We validated the results through systematic interviews with the operators of five of the networks. We found the metrics to be predictive of the issues operators face when reconfiguring their networks. A surprising result of our study was uncovering the reasons for operators choosing the designs they did.

Given the frequency with which configuration errors are responsible for major outages, we believe that creating techniques to quantify the complexity of a network's design is an important first step to reducing that complexity. In databases, software engineering and other fields, metrics and benchmarks have driven the direction of the field by defining what is desirable and what is not. In proposing these metrics, we hope to start a similar conversation for network design.

I will end the talk with a brief description of our recent work on WAN optimization.