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The southbound interface is situated between the controller and the devices on the virtualization plane. This signaling protocol passes the configuration commands in one direction and manages the statistical information feedback in the other. There are many open source proposals for some under development. An initial list of protocols for this southbound interface is:

 – OpenFlow from the ONF;

 – I2RS (Interface to Routing Systems) from the IETF;

 – Open vSwitch Data Base (OvSDB);

 – NetConf;

 – SNMP;

 – LISP;

 – BGP.

We will detail the most significant protocols in Chapter 4. However, to introduce this southbound interface, let us look at the most iconic protocol: OpenFlow. This signaling is shown in Figure 2.10. It takes place between the controller and the network devices. The data transported obey the trilogy “match-action-statistics” – in other words, we need to:

 – determine the streams uniquely by matching a certain number of elements such as addresses or port numbers;

 – specify the actions transmitted from the controller to the networking devices, such as updating a forwarding table or switch table, or, more generally, a forwarding device;

 – transfer tables containing statistics on the degree of use of the ports, transmission lines and nodes, such as the number of bytes sent through a given port.

This solution has been standardized by the ONF (Open Network Foundation), and we will describe it in greater detail in Chapter 4.

Figure 2.10. The signaling protocol OpenFlow