Cisco Systems Cisco Systems Ericsson APNIC Complexity is a widely used parameter in network design, yet there is no generally accepted definition of the term. Complexity metrics exist in a wide range of research papers, but most of these address only a particular aspect of a network, for example, the complexity of a graph or software. While it may be impossible to define a metric for overall network complexity, there is a desire to better understand the complexity of a network as a whole, as deployed today to provide Internet services. This document provides a framework to guide research on the topic of network complexity as well as some practical examples for trade-offs in networking. This document summarizes the work of the IRTF's Network Complexity Research Group (NCRG) at the time of its closure. It does not present final results, but a snapshot of an ongoing activity, as a basis for future work.