LAUSR

Software-defined networking is moving from its initial deployment in small-scale data center networks to large-scale carrier-grade networks. In such environments, high availability and scalability are two of the most prominent issues, and thus extensive work is ongoing. In this article, we first review the state of the art on high availability and scalability issues in SDN and investigate relevant open source activities. In particular, two well-known open source projects, OpenDaylight (ODL) and Open Network Operating System (ONOS), are analyzed in terms of high availability (i.e., network state database replication/synchronization and controller failover mechanisms) and scalability (i.e., network state database partition/ distribution and controller assignment mechanisms) issues. We also present experimental results on the flow rule installation/read throughput and the failover time upon a controller failure in ONOS and ODL, and identify open research challenges.