Interrelation between the software-defined and conventional IP-networks

Software-defined networking (SDN) is a centralized network control concept that postulates concentration of all control plane functions in a logically single programmatic network controller, simplification of data plane nodes to primitive switches, and a unified protocol, OpenFlow, particularly, of interaction between them and the controller. The SDN idea was born and initially implemented within academic laboratories. However, its expansion to data centers and, subsequently, to provider networks revealed a number of weak spots. The network bootstrapping and remote configuring were among them since these procedures cannot be accomplished using solely the OpenFlow means and do not fit into the original SDN framework. The SDN networks deployment practice showed the impracticability of the refusal from the TCP / IP protocol stack which remains indispensable, in particular, for SDN network bootstrapping and remote configuring. As a result, in the reality, we observe the SDN network nodes as some traditional full-fledged routers, only augmented with the supplementary OpenFlow functionality, instead of the conceptual simple pure OpenFlow switches, while the SDN networks themselves remain trivial IP networks with the centralized control being not full-sufficient and provided as an optional supplement.