Hey, You Darned Counters! Get Off My ASIC!

Software-Defined Networking (SDN) gains much of its value through the use of central controllers with global views of dynamic network state. To support a global view, SDN protocols, such as OpenFlow, expose several counters for each flow-table rule. These counters must be maintained by the data plane, which is typically implemented in hardware as an ASIC. ASIC-based counters are inflexible, and cannot easily be modified to compute novel metrics. These counters do not need to be on the ASIC. If the ASIC data plane has a fast connection to a general-purpose CPU with cost-effective memory, the authors can replace traditional counters with a stream of rule-match records, transmit this stream to the CPU, and then process the stream in the CPU.