Understanding OpenFlow
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This document provides a technical overview of OpenFlow Switch Specification version 1.0.0 published in 2009. It discusses how OpenFlow addresses the requirements for software-defined networking by defining a common logical architecture for network devices and a standard communication protocol. The key components of OpenFlow are flow tables within each device to manage packet flows through actions on matched rules, and a secure channel protocol for an SDN controller to communicate with OpenFlow devices and modify flow entries.
Understanding OpenFlow
- 1. Understanding OpenFlow Technical Whitepaper June, 2014 Saurabh Kumar Agarwal Email: [email protected]
- 2. Understanding OpenFlow | Technical Whitepaper Abstract Technical overview of OpenFlow Switch Specification, Version 1.0.0, published on December 31, 2009 by Open Networking Foundation. Introduction OpenFlow protocol addresses the two key requirements needed to turn the concept of SDN into practical implementation. First, there must be a common logical architecture in all network devices to be managed by an SDN controller. needed between the SDN controller and the network device. OpenFlow is defined in the OpenFlow Switch Specification, published by the Open Networking Foundation (ONF). ONF is a consortium of software providers, conten networks, and networking equipment vendors whose purpose is to promote SDN. This paper discusses the basic technical aspects of OpenFlow 1.0.0 Traditional Vs. OpenFlow Based There is a distinct difference between how switching happens and how OpenFlow proposes to change it. To further understand the concepts of OpenFlow it is important to know this difference. Traditional Switching Switching traditionally at L2 level has always been done using MAC addresses. Eac maintains its own MAC table based on which it learns where other devices are located. 1. Client 1 sends data to Client 2 2. Frame arrives at Switch A with MAC = 3. MAC address table is checked for location of 4. Entry is found in forwarding table 5. Frame is transmitted out of Second, a standard, secure protocol is Networks in traditional networks EEEE:EEEE:EEEE to MAC = FFFF:FFFF:FFFF MAC FFFF:FFFF:FFFF P2 content delivery Each device
- 3. Understanding OpenFlow | Technical Whitepaper OpenFlow Switching Switching in OpenFlow based networks is done using flows instead of MAC or IP tables. Each flow entry has rules and actions corresponding to it. When the corresponding action is taken by device. Every flow in OpenFlow has three parts to it: 1. Rule – This is what defines the flow and carries information for packet matching. 2. Action – What you want switch to do on rule match? There are OpenFlow supports: a. Forward – Forward to the output port b. Drop – Drop the packets c. Redirect – Encapsulate the packet and redirect to SDN Controller. OpenFlow Components An SDN controller communicates with OpenFlow protocol running over the Secure Sockets Layer (SSL). Each OpenFlow devices and, possibly, to end of packet flows. Within each device or firmware—are used to manage the flows of packets through the So the major two components of OpenFlow are, rule is satisfied, the three actions that OpenFlow-compatible devices using the OpenFlow device connects to other end-user devices that are the sources and destinations device, a series of tables—typically implemented in hardware device. lly Flow Table and Secure Channel Protocol Protocol.
- 4. Understanding OpenFlow | Technical Whitepaper Flow Table The basic building block of OpenFlow is the flow table. E passes through one or more flow tables. Flow t Header Field Each packet that enters a device table has following three things. Action Counters Header Field Each flow table header entry is made up of six components, which defined the matching rules and other basic rules for the corresponding flow. Action Each flow entry is associated with zero or more actions that dictate how the device handles matching packets. Actions in OpenFlow specification are defined as required and optional. Optional actions are e not required to be implemented by vendors as such. ach
- 5. Understanding OpenFlow | Technical Whitepaper Counters Counters are maintained per-table, per-per flow, per-port and per queue. There are a set of required counters that all the implementations should support and there are additionally optional counters. Flow Matching Example A sample packet flow matching flowchart is below explaining how the packet matching is done with OpenFlow 1.0.0.
- 6. Understanding OpenFlow | Technical Whitepaper Secure Channel The OpenFlow protocol describes message exchanges that take place between an OpenFlow controller and an OpenFlow device. device Typically, the protocol is implemented on top of SSL or Transport Layer Security (TLS), providing a secure OpenFlow channel. The OpenFlow protocol enables the controller to perform add, update, and delete actions to the flow entries s in the flow tables. tables It supports three types of messages: 1. Controller-to-Device: : These messages are initiated by the controller and, in some cases, require a response from the device. 2. Asynchronous: These types of messages are sent without solicitation from the controller. 3. Symmetric: These messages are sent without solicitation from either the controller or the device. . They are simple yet helpful. Below is the list of complete OpenFlow messages th support. that any implementation needs to . at
- 7. OpenFlow Communication Example Below is a example of how OpenFlow communication is setup and maintained with which is OpenFlow enabled. References Open Networking Foundation OpenFlow 1.0.0 Specification Understanding OpenFlow | Technical Whitepaper a switch