Modeling Complexity of Enterprise Routing Design

Enterprise networks often have complex routing designs given the need to meet a wide set of resiliency, security and routing policies. In this paper, we take the position that minimizing design com-plexity must be an explicit objective of routing design. We take a first step to this end by presenting a systematic approach for mod-eling and reasoning about complexity in enterprise routing design. We make three contributions. First, we present a framework for precisely defining objectives of routing design, and for reasoning about how a combination of routing design primitives (e.g. rout-ing instances, static routes, and route filters etc.) will meet the objectives. Second, we show that it is feasible to quantitatively measure the complexity of a routing design by modeling individual routing design primitives, and leveraging configuration complexity metrics [5]. Our approach helps understand how individual design choices made by operators impact configuration complexity, and can enable quantifying design complexity in the absence of con-figuration files. Third, we validate our model and demonstrate its utility through a longitudinal analysis of the evolution of the rout-ing design of a large campus network over the last three years. We show how our models can enable comparison of the complexity of multiple routing designs that meet the same objective, guide op-erators in making design choices that can lower complexity, and enable what-if analysis to assess the potential impact of a configu-ration change on routing design complexity