Challenges in the emulation of large scale software defined networks

Researchers and practitioners alike have long relied upon emulation to evaluate the performance of networked applications and protocols without tying up production infrastructure or committing to expensive hardware purchases. As software defined networks (SDN) become more prevalent, it is increasingly useful to be able to accurately emulate their behavior. Tools like Mininet-HiFi have demonstrated the viability of small-scale SDN emulation, but emulated network size is limited by the hardware resources of a single machine. Unfortunately, there are many SDN applications that can only be evaluated meaningfully at scale. Traditionally, researchers have overcome similar challenges by scaling the capacity of the network links, the emulated workload, or both. We observe that shrinking a network arbitrarily to fit into a fixed set of emulation resources has fundamental limitations that impact the fidelity of results, especially in the context of SDN. In particular, we demonstrate cases where emulation yields false positives---poor network behavior that manifests only in emulation---and false negatives, where a real deployment would suffer issues not apparent in emulation. We discuss strategies that might be used to combat these effects and their limitations.