Deployment Guide

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3.3 Overview – What is DNOS-OF?
As a product line, the Dell Networking Operating System – for OpenFlow, DNOS-OF is a firmware bundle
that allows a traditional N series switch to be used as a pure OpenFlow switch. DNOS-OF is designed to
1. Deliver a pure OpenFlow switch for the N series
2. Enable SDN in campus networks
3. Interoperate with any controller supporting OpenFlow 1.3.4 and multiple table support.
DNOS-OF leverages the BigSwitch Networks open source Indigo agent (Indigo) and Broadcom’s
OpenFlow Data Plane Abstraction (OF-DPA) packages to provide OpenFlow support.
The DNOS-OF based abstract switch is a specialization of the OpenFlow 1.3.4 OFLS (OpenFlow logical
switch). Section 4.3.1 below describes the DNOS-OF Abstract Switch in terms of abstract objects that are
visible to the OpenFlow controller.
The DNOS-OF abstract switch objects can be thought of as programming points for the Ethernet
switching hardware. These include flow tables with action sets, group table entries, physical ports, and
queues. The DNOS-OF adaptation layer provides support for OpenFlow specific state, for example,
statistics counters. It also maps OpenFlow objects to hardware and manages hardware resources.
Supporting OpenFlow in switch hardware involves some tradeoffs. As has been noted elsewhere, the
generality promised by OpenFlow can come at a cost of latency, as well as cost and power inefficiencies.
In addition, to effectively use this generality a specific multi-table pipeline first needs to be designed and
configured. The DNOS-OF Abstract Switch may be viewed as coming preconfigured and optimized to
support single pass, full bandwidth packet processing performance that makes efficient use of the
hardware and available table memory resources, trading off unrestricted generality in favor of latency,
performance, and cost, while enabling a logically centralized control plane with programming flexibility.
The DNOS-OF Abstract Switch includes functionality to support bridging and routing functionality on the
switch chip, among others. These flows expose the proper functionality in the switching hardware. Future
versions of DNOS-OF are expected to support additional features and packet flow use cases.
DNOS-OF implements a basic SDK switch OS with primary functionality being an SDN agent, a CLI and
platform support for the various N-Series hardware components.