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Published on Nov 20, 2015
Presented by: Gal Sagie, Huawei; Liran Schour, IBM
In this talk we discuss the need to enable flexible construction of the OVN processing pipeline. In addition, we describe an example where this feature can be used and propose a path to implementation. Currently, OVN implements a fixed logical pipeline composed from several stages. Each pipeline stage, assigned with a unique table id, is translated into a flow table configured on every OVS instance by the ovn-controller. In some cases, however, an external entity with out-of-band knowledge needs to impose workflow-specific actions on some flows. To grow the OVN ecosystem, it can be beneficial to enable 3rd party components to change the logical pipeline by adding new stages.
We describe an example of such a component that detects elephant flows by sflow monitoring from overlay edges and marks them for differentiated processing in the physical forwarding plane. When detected, elephant flows are being marked by adding logical flows that set DSCP field to a specific value. Physical forwarding plane then uses these marks to separate elephants flows from the rest, e.g. by sending them over ad-hoc optical circuits or over specialized DCI links. Implementation-wise, we propose to extend the current fixed logical pipeline to be flexible by providing a SB control API whereby entities external to the OVN control plane can add new pipeline stages. As a result, external loosely coupled entities will be be able to define new flow tables where workload-specific logical flows can be added.
We will also describe another approach that allows reactiveness in the model and hence simpler to develop more sophisticated external network services and applications, and how it can be implemented in OVN.