Software Defined Networks (SDN) separate the control plane from the data plane in network nodes, allowing for centralized control and programmability. The Open Flow protocol allows an external controller to communicate with SDN-enabled switches to program their flow tables and direct traffic. This provides benefits like increased flexibility, automation, and innovation compared to traditional networks where control and forwarding are coupled in closed hardware devices.

1. Software Defined Networks
and Open flow Protocol
Mahesh M
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2. Introduction to SDN
 An innovative approach to network architecture that provides the ability to
create a whole new class of functionality
 Experimental
 Separates the data plane and the control plane of nodes
 Nodes will only be forwarding the information
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3. Why SDN?
 Network – Core element of an organization’s technology service
 Current Scenario
 Several discrete network devices require manual configuration and
management
 These devices will be closed, proprietary units that limit innovation
 Hence extensibility close to zero
 Need for a New network?
 Change in traffic patterns
 The “consumerisation of IT”
 Rise of cloud services
 Big Data => requirement of more bandwidth
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4. Transition to SDN…
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Features Features
Operating System
Specialized
packet
forwarding
hardware
Features Features
Operating System
Specialized
packet
forwarding
hardware
Features Features
Operating System
Specialized
packet
forwarding
hardware

5. Transition to SDN…
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packet forwarding
Features Features
Network Operating System
Control Plane
Data Plane
Open Flow Protocol
packet forwarding
packet forwarding

6. What is SDN?
 A flexible network architecture
 Control plane and Data plane – core components of a network switch
 Current devices have both control and data plane residing on the
physical switch
 SDN - Control plane separated from the data plane and placed on a
server
 Software application – provides direction to data plane
 Interaction between controller and data plane – using Open Flow protocol
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7. Open Flow Protocol
 TCP based
 Maintained by the open networking foundation
 Provides numerous functions and commands for
 Communication of data
 Status and management of the devices
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8. Open Flow Protocol
 Basic idea – use of flow tables as in Ethernet switches
 Flow Tables – vendor specific
 OFP : provides an open protocol to program the flow table in different switches
and routers
 In a OFP : data path consists of flow table
 An action will be associated with a flow entry
 Set of actions supported by the open flow is extensible
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9. The Open Flow Switch  Consists of at least 3 parts
 A flow table – an action associated with each
flow entry
 A secure channel – connects the switch to a
remote control process(controller)
 Open Flow Protocol – Open and standard way
for a controller to communicate with a switch
 Types
 Dedicated OF switches
 Open Flow Enabled switches
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10. OFP – How it works?
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Controller
Node 4
Node 2
Node 3
Flow
Table
If matchfield : forward message to node 4
If matchfield : change header and forward to node 2

11. Flow Table
 Consists of flow entries
 Each flow entry has
 Match fields
 Counters – update the number of matching packets
 Set of instructions to apply to matching packets
 Matching starts from 1st flow table and may continue to other flow tables
 Matching done in priority order – first match is used
 If no match – may continue to next flow table or may be forwarded to the
controller via OFP or packet can be dropped – depends on the switch configuration
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12. 11/27/2015Software Defined Networks and Open Flow Protocol
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Flowchart detailing packet flow through an Open
Flow switch

13. Instructions
 Each flow entry include set of instructions that are executed when a packet
matches the entry
 Supported instructions
 Apply-Actions action
 Clear-Action
 Write-Action actions
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14. Open Flow Channel
 Connects each open flow switch to the controller
 Usually encrypted using TLS, but may be run directly over TCP
PROTOCOL OVERVIEW
 Support 3 messages
 Controller to switch
 Asynchronous
 symmetric
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15. Controller to Switch
 Initiated by the controller
 Message types
 Features : Controller may request for the features of the switch – expects a features reply with
available capabilities of the switch
 Configuration : controller set/query conffig parameters
 Modify State : manages state on the switches – mainly to add/delete/modify flow entries
 Read State : to collect sttistics from the switch
 Packet-out : used to send packets out of a specied port on the switch, and to forward packets
received via Packet-in messages
 Barrier : to ensure message dependencies have been met or to receive notications for
completed operations
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16. Asynchronous
 Switches send these to indicate packet arrival, switch state change or error
 Message types:
 Packet In : For all packets that do not have a matching row entry, a packet-in event may
be sent to the controller
 Flow removed
 Port status
 Error
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17. Synchronous
 sent without solicitation, in either direction
 Hello: Hello messages are exchanged between the switch and controller upon connection
startup
 Echo : used to measure the latency or bandwidth of a controller-switch connection, as
well as verify its liveness
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18. Open Flow Channel Connection setup
 Switch must be able to connect to a known IP via a user specified port
 If IP is known – switch initiates a TLS or TCP connection to the controller
 After connection is established each side should send a OFTP_Hello message with
the version number
 If version supported connection proceeds
 Else – reply OFPT_Error with
 with a type field of OFPET_HELLO_FAILED,
 a code field of OFPHFC_COMPATIBLE, and
 optionally an ASCII string explaining the situation in data,
And terminate the connection
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19. Connection Interruption
 Switch may lose connection due to
 Echo request timeout
 TLS session timeout
 Or other disconnections
 Switch should contact one or more backup controllers – not specified in the
protocol
 Two modes
 Fail Secure – packets and messages destined to current controller is dropped
 Fail standalone – Switch act as a legacy Ethernet switch or router – processes all the
packets by itself
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20. Encryption and Message Handling
 Encryption
 Communication through TLS connection
 TLS initiated by switch during the startup
 Controller and switch mutually authenticate using certificates
 Controller Certificate
 Switch Certificate
 Message Handling
 OFP provide reliable message delivery and processing
 Does not provide automatic acknowledgements
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21. Benefits of Open flow SDN
 Centralized control of multi-vendor environments
 Reduced complexity through automation
 Higher rate of innovation
 Increased network reliability and security
 More granular network control
 Better user experience
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22. Summary
 Current networks - less extensible
 Solution - Software Defined Networking and Open Flow protocol
 SDN – Emerging technology
 Separates data and control planes
 Makes the network control centralized
 Network devices are only packet forwarding objects
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23. References
 OpenFlow Switch Specication, Version 1.1.0 Implemented (Wire Protocol 0x02 ),
February 28, 2011 – The Open Networking Foundation
 Software-Defined Networking: The New Norm for Networks, ONF White Paper, April 13,
2012
 Zanna, P.; Hosseini, S.; Radcliffe, P.; O'Neill, B., "The challenges of deploying a software
defined network," in Telecommunication Networks and Applications Conference
(ATNAC), 2014 Australasian , vol., no., pp.111-116, 26-28 Nov. 2014
doi: 10.1109/ATNAC.2014.7020883
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7020883&isnumber=7
020854
 Jian-Quan Wang; Haijing Fu; Chang Cao, "Software defined networking for telecom
operators: Architecture and applications," in Communications and Networking in China
(CHINACOM), 2013 8th International ICST Conference on , vol., no., pp.828-833, 14-16
Aug. 2013
doi: 10.1109/ChinaCom.2013.6694710
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6694710&isnumber=6
694549
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