The network and distributed systems research communities have an increasing need for “replayable” research, but our current experimentation resources fall short of reaching this goal. Replayable activities are those that can be re-executed, either as-is or in modified form, yielding new results that can be compared to previously obtained results. Replayability requires complete records of experiment processes and data, of course, but it also requires facilities that allow those processes to actually be examined, repeated, modified, and reused for new studies. We are now evolving Emulab, our popular network testbed management system, to be the basis of a new “experimentation workbench” in support of realistic, largescale, replayable networking research. We have implemented a new model of testbed-based experiments, based on scientific workflow, that allows people to move forward and backward through their experimentation processes. Integrated tools in the workbench help rese...