Logical SDNs: Reaping Software-Defined Networking Benefits Through Incremental Deployment

Although SDN promises principled approaches to longstanding network operations problems, with the exception of a few notable deployments in the wild, e.g., Google’s B4, it remains largely an experimental technology for most organizations. As the transition of existing networks to SDN will not be instantaneous, we consider hybrid networks that combine SDN and legacy networking devices an important avenue of research; yet research focusing on these environments has so far been modest. Hybrid networks posses practical importance, are likely to be a problem that will span years, and present a host of interesting challenges, including the need for radically different networking paradigms to not only co-exist, but also offer clear, immediate benefits. We argue that an appealing approach to hybrid networking can be achieved by introducing SDN devices into existing networks and abstracting the legacy network devices away as “expensive wires” to expose a programmatic “logical SDN” interface — conceptually, a representation of the network limited to just the SDN devices. Motivated by the need to better understand the potential and limits for the logical SDN abstraction for hybrid networks, in this work, we showcase the power and utility of the logical SDN by reasoning through and implementing use-case control applications built on this abstraction. Realizing this abstraction comes at the cost however, of diverting traffic from legacy switches through SDN devices. We thus explore the impact of the logical SDN on the network traffic flow performance through experiments in a high-performance emulation environment.