I just read an article from Greg Ferro about Integerating Overlay and Physical Networks http://etherealmind.com/integrating-overlay-networking-and-the-physical-network/?utm_source=feedly&utm_medium=feed&utm_campaign=Feed%3A+etherealmind+%28My+Etherealmind+-+Network+design%2C+architecture%2C+thinking%2C+working.+Tech.%29 which is a nice compliment to an interesting demo I just saw at Cisco Live. The demo showed how the XNC can be used to manage an Overlay/Underlay network using OpenFlow to manage the traffic flows between OVS instances with GRE tunnels (overlay), and onePK to manage the physical network (underlay).
For instance, you may have traffic that needs low latency, and other traffic that needs maximum bandwidth. You could specify these two types of flows using the TIF (Topology Indpenednet Forwading) feature on the controller. Then you could tie them to “IPSLA” tags that will indicate to the controller what characteristics the traffic wants. The controller is aware of both the overlay and underlay networks, and can coordinate the configuration between them. OnePK is used to inject “application routes” into the underlay network that dictate which path the GRE tunnels take, based on the same tags used in the OpenFlow configuration.
I hope to grab some screenshots and add them to this post, but this seems like a cool use case for the controller. I also hope that some of this functionality will make its way into OpenDaylight.