This document introduces container networking and some of the challenges it poses. It discusses how Docker's default bridge networking works but has limitations around port constraints and lack of "real IP networking". Overlay networks are presented as an alternative but have drawbacks around state, isolation between networks, and requiring developers to be networking experts. Project Calico is then introduced as an open source project that aims to enable scalable, simple and secure IP networking for containers through features like equal cost multi-path routing and rich micro-service policy frameworks.