Which flows are hiding behind my wildcard rule?: adding packet sampling to openflow

In OpenFlow, multiple switches share the same control plane which is centralized at what is called the OpenFlow controller. A switch only consists of a forwarding plane. Rules for forwarding individual packets (called flow entries in OpenFlow) are pushed from the controller to the switches. In a network with a high arrival rate of new flows, such as in a data center, the control traffic between the switch and controller can become very high. As a consequence, routing of new flows will be slow. One way to reduce control traffic is to use wildcarded flow entries. Wildcard flow entries can be used to create default routes in the network. However, since switches do not keep track of flows covered by a wildcard flow entry, the controller no longer has knowledge about individual flows. To find out about these individual flows we propose an extension to the current OpenFlow standard to enable packet sampling of wildcard flow entries.