28 Software Networks
2.5. Southbound interface
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 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);
– Net Conf;
– SNMP;
– LISP;
– BGP.
We shall detail the most significant protocols in the next chapter.
However, to introduce this southbound interface, let us look at the
most iconic protocol: OpenFlow. This signaling is illustrated in
Figure 2.10. It takes place between the controller and the network
devices. The data transported obey the trilogy “match-actionstatistics”– 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 the rows in 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 shall describe it in greater detail in the next
chapter.
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