The OpenFlow standard accommodates network control traffic by providing packet in and out messages for sending packets between the network and controller. We conduct comprehensive measurements of the performance of this control architecture in different configurations across five hardware switches, each from a different vendor, representing a broad range of OpenFlow offerings, from implementations built on legacy ASIC architectures, to those implemented solely with OpenFlow in mind. The best performing switch achieved a maximum mean packet-in rate of 5,145 messages per second, representing less than 3Mbps of traffic. Additionally, all switches tested failed to maintain control traffic latency under 50ms in one or more tests. We find the slow-path performance of these hardware switches is easily overloaded and is insufficient for modern network control architectures.