Saturday, November 21, 2015

OVN service injection demonstration

Enabling extensibility in OVN, by Gal Sagie, Huawei and Liran Schour, IBM, Open vSwitch 2015 Fall Conference describes a method for composing actions from an external application with actions installed by the Open Network Virtualization (OVN) controller.

An API allows services to be attached to logical topology elements in the OVN logical topology, resulting in a table in the OVN logical flow table that is under the controller of the external service. Changes to the logical table are then automatically instantiated as concrete flows in the Open vSwitch instances responsible for handling the packets in the flow.

The demo presented involves detecting large "Elephant" flows using sFlow instrumentation embedded in Open vSwitch. Once a large flow is detected, logical flows are instantiated in the OVN controller to mark the packets. The concrete marking rules are inserted in the Open vSwitch packet processing pipelines handling the logical flow's packets. In the demo, the marked packets are then diverted by the physical network to a dedicated optical circuit.

There are a number of interesting traffic control use cases described on this blog that could leverage the capabilities of Open vSwitch using this approach:
The logical flow abstraction implemented by OVN greatly simplifies the problem of composing policies needed to integrate service injection and chaining within the packet pipeline and is a very promising platform for tackling this class of problem.

Many service injection use cases, including the hybrid packet/optical case demonstrated in this talk, need to be informed by measurements made throughout the network, for example, you wouldn't want to divert traffic to the optical link if it was already at capacity. New OVS instrumentation features aimed at real-time monitoring of virtual networks, another talk from the Open vSwitch conference, describes how sFlow measurements from Open vSwitch and physical network switches can be combined to provide the comprehensive visibility needed for this type of traffic control.
There are significant advantages to applying service injection actions in the virtual switches, primarily avoiding the resource constraints imposed by physical hardware that limit the number of and types of rules that can be applied. However, some services are location dependent and so the external application may need direct access to the injected table on the individual virtual switches. This could be achieved by exposing the tables through the OVN daemons running on the hypervisors, or directly via OpenFlow connections to the Open vSwitch instances to allow the external application to control only the tables created for it.

The OpenFlow approach could be implemented through the OVN Northbound database, attaching the external service specific tables to the virtual network topology and assigning an OpenFlow controller to manage those tables. Once the changes propagate down to the vSwitches, they will create an additional OpenFlow connection to the designated controller that expose the assigned table. This notion of "slicing" resources is one of the earliest use cases for OpenFlow, see FlowVisor. In addition to supporting location dependent use cases, this approach offloads runtime control of delegated tables from OVN, decoupling the performance of the injected services from OVN applied controls.

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