What is Inter-Instance Complexity

Networks with higher degrees of complexity typically require more effort to manage and are more prone to configuration errors. Unfortunately, complexity remains one of the least understood aspects of networking. This chapter takes a first step toward bridging this gap, by presenting a top-down framework for modeling complexity in routing design, a critical and highly complex network design task. First, a set of abstractions is introduced for precisely defining objectives of routing design, and for reasoning about how a combination of routing design primitives will meet the objectives. Next, models are presented for quantitatively measuring the complexity of a routing design by modeling individual design primitives and leveraging configuration-derived complexity metrics. This modeling approach helps understand how individual design choices may impact the resulting complexity, and enables comparison of alternative routing designs and “what-if” analysis of the potential impact of a design change on complexity.