In a software-defined network (SDN) architecture, southbound application program interfaces (APIs) (or SDN southbound APIs) are used to communicate between the SDN Controller and the switches and routers of the network. They can be open or proprietary.
How Do SDN Southbound APIs Work?
Southbound APIs facilitate efficient control over the network and enable the SDN Controller to dynamically make changes according to real-time demands and needs. OpenFlow, which was developed by the Open Networking Foundation (ONF), is the first and probably most well-known southbound interface. It is an industry standard that defines the way the SDN Controller should interact with the forwarding plane to make adjustments to the network, so it can better adapt to changing business requirements. With OpenFlow, entries can be added and removed to the internal flow-table of switches and potentially routers to make the network more responsive to real-time traffic demands. Besides OpenFlow, Cisco OpFlex (the company’s response to OpenFlow) is also a well-known southbound API.
There are a number of switch and router vendors that have announced their support of OpenFlow, including Cisco, Juniper, Big Switch Networks, Brocade, Arista, Extreme Networks, IBM, Dell, NoviFlow, HP, NEC, among others.
While OpenFlow is the most well-known of the SDN protocols for southbound APIs, it is not the only one available or in development. The Network Configuration Protocol (NetConf) uses an Extensible Markup Language (XML) to communicate with the switches and routers to install and make configuration changes; Lisp, also promoted by ONF, is available to support flow mapping. In addition, there are more established networking protocols finding ways to run in an SDN environment, such as OSPF, MPLS, BGP, and IS-IS.