The Docker network overlay driver relies on several technologies: network namespaces, VXLAN, Netlink and a distributed key-value store. This talk will present each of these mechanisms one by one along with their userland tools and show hands-on how they interact together when setting up an overlay to connect containers. The talk will continue with a demo showing how to build your own simple overlay using these technologies. Finally it will show how we can dynamically distribute IP and MAC information to every hosts in the overlay.