UNIT I

1 SDN :Introduction
Syllabus
Evohing Nerwork Requirements - The SDNApproach -SDN architecture - SDN Data Plane, Control
plane and Application Plane

Contents
1.1 Evolving Network Requirements
1.2 The SDN Approach
1.3 SDN Data Plane, Control plane and Application Plane
1.4 Two Marks Questions with Answers

(1-1)
Softwane Defined Networks 1-2 SDN: Introduction

1.1 Evolving Network Requirements

. As businesses have grown more dependent on networks for success, network
anchitectures have evolved over the years. Traditionally, users, data and applications
were houscd on premise. Uscrs could only access network resources with company
owned computers. The network had distinct borders and access requirements.
Maintaining security, productivity and services was simpler.
. Today, the network border has shifted, creating new challenges for IT departments.
Networks are transforming from a data-only transportation system of connected LAN
devices to a system that enables the connections of people, devices and information in a
media-rich, converged network environment.
As new technologies and end-user devices come to market, businesses and consumers
must continue to adjust to this ever-changing environment. There are several new
networking trends that continue to effect organizations and consumers.
" A number of trends are driving network providers and users to reevaluate traditional
approaches to network architecture. These trends can be grouped under the categories of
demand, supply and traffic patterns.
1. Inerease in demand : Number of trends are increasing the load on enterprise
networks, the Internet and other internets. Let us consider following:
a) Cloud computing : Most of organizations are shifted on both public and private
cloud services.
b) Big data : The processing of huge data sets requires masive parallel processing
on thousands of servers, all of which require a degree of interconnection to each
other. Therefore, there is a large and constantly growing demand for network
capacity within the data canter.
) Mobile traffie : Employees are increasingly accessing enterprise network
resources via mobile personal devices, such as smartphones, tablets and
notebooks. These devices support sophisticated apps that can consume and
generate image and video traffic, placing new burdens on the enterprise
Detwork.
d) The Internet of Things (loT) : Most "hings" in the loT generate modeSst
Iraflic, altough there are exceptions, such as surveillance video cameras. There
is a signilicant load on the enterprise network
2. Supply Is Increasing : As the demand on networks is inerease, so is the capaciy o
network technologies to absorb rising loads.

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Software Defined Networks 1-3 SDN: Introduction
The increase in the capacity of the network transmission technologies has been
matched by an increase in the performance of network devices, such as LAN
switches, routers, firewalls, IDS / IPS and network monitoring and management
systems.
Day by day, these devices have larger, faster memories, enabling greater buffer
capacity and faster buffer access, as well as faster processor speeds.
3. Traditional network architectures are inadequate
The traditional internetworking approach is based on the TCP/IP protocol
architecture.
Traditionally, routing was based on cach packet's destination address. In this
datagram approach, successive packets between a source and destination may
follow different routes through the internet, as routers constantly seek to find the
minimum-delay path for each individual packet.
A datagram carries information sufficient for routing from the source to the
destination without the necessity of establishing a logical connection between
the endpoints.
Apacket is a group of bits that includes data plus protocol control information.
1.1.1 Challenges of Traditional Networks
" The most common way of networking, traditional networking, uses fixed-function and
dedicated hardware and network devices, including switches and routers, to control
network traffic. These devices have individual functions that work well together and
help to support the network.
The ability to scale is a frequent problem for traditional networks. Most switching
hardware and software is proprietary and it is uncommon for APIs to be expOsed for
provisioning.
. Traditional networks tend to synergize well with proprietary provisioning software.
Unfortunately for traditional networks, this software is unable to be modified as needed
and hardware-centric networking can be very limiting in
what it is able to use.
In a traditional router or switch architecture,
both the control and data plane function on
a single device.
" Traditional networking's functions and functionality are
ways : implemented in the following
a) The functions are
implemented from dedicated devices that use switches, routers and
application delivery controls.
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Soar Deint Nehorks f4 SDN: Introduction

b The functionality is primarily implemented in application-specific integrated circuits

(ASIC) and other dedicated hardware.
Neworks continue to expand and become more complex as network infrastructure
enlarges. In addition, new users and network services are constantly being added to the
network. Both new users and network services demand huge network resources, which
is increasing exponentially.
With regards to increasing size and complexity of networks, traditional approaches for
nework management would be highly inefficient. This places a serious strain on
nerwork operators as they are faced with the task of implementing diverse
configurations and keeping track of innumerous events on the network.
Traditional networks face a constant challenge in terms of flexibility. Provisioning APls
are few and most switching hardware and software are proprietary. Traditional networks
often operate effectively with proprietary provisioning software; however, this software
cannot be changed as quickly as needed.
" Traditional networking consists of the following traits:
1. Traditional networking functions are typically perfomed by dedicated devices like as
switches, routers and application delivery controllers, which use one or more
Switches.

2. Traditional networking functions are mostly implemented in dedicated hardware,

such as application-specific integrated circuits (ASIC). The restrictions of traditional
hardware-centric networking are one of its drawbacks.
The networks were static in nature and were manually configured based on service
requests.

In a traditional network, on the other hand, the physical placement .of the control plane
makes it difficult for an IT administrator to control traffic flow.
In traditional network architecture, the control plane and data plane are integrated. Any
changes to the system are dependent upon configuring physical network devices, the
prutocols and software they support.
" The control plane becomes software-based with SDN, making it accessible via a
connected device. This access allows IT managers to better manage traffic flow from a
centralzed User Interface (Ul). Users have more control over how their networks run
and are set up thanks to this one place. For network segmentation, the ability to Switly
process rul1ple network configurations from acentralized Ul is extremely useful.

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Software Defined Networks 1-5 SDN: Introduction

1.2 The SDN Approach

SDN requirements are as follows :
1. Adaptability : Networks must adjust and respond dynamically, based on application
needs, business policy, and network conditions.
2. Automation : Policy changes must be automatically propagated so that manual work
and errors can be reduced.
3. Maintainability : Introduction of nevw features and capabilities (software upgrades,
patches) must be seamless with minimal disruption of operations.
4. Model management : Network management software must allow management of
the network at a model level, rather than implementing conceptual changes by
reconfiguring individual network elements.
S. Mobility : Control functionality must accommodate mobility, including mobile user
devices and virtual servers.

6. Integrated security : Network applications must integrate seamless security as a

core service instead of as an add-on solution.
7. On-demand scaling : Implementations must have the ability to scale up or scale
down the network and its services to support on-demand requests.

1.2.1 SDN Architecture

SDN architecture defines how a networking and computing system can be designed to
use a mix of open, software-based technologies with commodity networking hardware.
" SDN architecture separates the control and data planes of the network stack.
The OpenFlow protocol is an open source way to have the different planes of a network
communicate.
" SDN controllers communicate with applications via the northbound API and with the
network infrastructure via southbound APls.
" Fig. 1.2.1 shows SDN architecture.

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Software Defined Networks 1-6 SDN: Introduction
Application layer

Network Network
application application

Northbound interface

Control layer (Control plane)

Network services

Southbound interface
(OpenFlow, ForCES, etc)
Infrastructure layer
(Data plane)

Fig. 1.2.1 SDN architecture

SDN components are : Data plane, control plan, Soundbound Interface, Northbound
Interface and Application Plane.
1. A controller, the core element of an SDN architecture, that enables
centralized
management and control, automation and policy enforcement across physical and
virtual network environments. The control of all the data plane devices are done via
SDN controllers. It also controls the applications at application layer. SDN
controller
communicate and control these upper and lower layers with APls through Interfaces.
2. Southbound APIs that relay information between the controller and the
individual
network devices (such as switches, access points, routers, and firéwalls).
3. Northbound APIs that relay information between the controller and the
applications
and policy engines, to which an SDN looks like a single logical network device.
4. Data plane is consists of various network devices both physical and
virtual. The main
duty of data plane is forwarding.
SDN WOrking :
" A software defined network uses a centralized SDN controller to deliver
software-based
network services. A network administrator can manage network policies from a central
control plane without having to handle individual switches.

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Software Defined Networks 1-7 SDN : Introduction

" SDN anchitecture has three layers that communicate vía northbound and southbound
Application Programming Interfaces (APIs). Applications can use a northbound
interface to talk to the controller. Meanwhile, the controller and switches can use
southbound interfaces to communicate.
The layers include :

1. Application layer : SDN applications communicate behaviors and needed resources

with the SDN controller.
2. Control layer manages policies and traffic flow. The centralized controller manages
data plane behavior.
3. Infrastructure layer consists of the physical switches in the network.
1.2.2 Characteristics of SDN
The first fundamental characteristic of SDN is the separation of the forwarding and
control planes. toordiahhou ¡ Muthple Sote/
Network orchestration : Orchestration of network resources increases your service
agility while çeducingoperational overheads.
Open interfaces are defined between the devices in the control plane and those in the
data plane.
The network is programmable by applications running on top of the SDN controllers.
The SDN controllers present an abstract view of network resources to the applications.
" A characteristic of Open SDN is that its interfaces should remain standard, well
documented and not proprietary.
1.2.3 Diferences between Traditional Networking and SDN
Sr. No. Traditional networking SDN
1. Traditional networking is usually SDN is software-based.
hardware-based.
2 Traditional networking has a distributed SDN has logically centralized control plane.
control plane.
3 It works using protocols SDN uses APls to configure as per nced.
4
Traditional networking are static and SDN are programmable networks during
inflcxible networks. deploynment time as well as at later stage
based on change in the requirements.
5. Traditional nctworking are not useful for SDN help new business ventures through
new business ventures. They possess little
agility and flexibility.
flexibility, agility and virtualization.

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Software Defined Networks 1-8 SDN: Introduction

6. With a traditional network the physical When SDN virtualizes entire network it
location of the control plane hinders an IT generates an abstract copy of physical
administrator's ability to control the network and lets we provision resources
traffic flow. from a centralized location.

7. In traditional network architecture, the SDN decouples the control plane from the
control plane and data plane are data plane.
integrated.

1.2.4 History of Software Defined Networking

Over the past two decades, networks have come under increased traffic demands and
increased scrutiny as both organizations and consumers increasingly rely on network
connectivity for sales, customer service, internal communications and document
sharing.
Traditional network architectures are not designed in a way that meets current
requirements. SDNs offer an alternative paradigm for meeting the needs of users,
companies and service providers.
In SDNs, the control plane communicates via a southbound interface with all devices on
the network, maintains a holistic view of the network's topology and programs the
network from a central point.
OpenFlow is the first standard communication protocol that interfaces between network
devices and the SDN controller.
" Software-Defined Networking (SDN) is a network architecture approach that enables
the network to be intelligently and centrally controlled, or 'programmed,' using software
applications. This helps operators manage the entire network consistently and
holistically, regardless of the underlying nctwork technology.
Software-defined networking is an architecture designed to make a network more
flexible and easier to manage. SDN centralizes management by abstracting the control
plane from the data forwarding function in the discrete networking devices.
SDN is important because it gives network operators new ways to design,
bmla au
operate their networks. Software-defined networking paired with network functions
virtualization is a key technology necded to meet new demands.
" SDN separates the nctwork's control and forwarding planes and provides a centralized
vicw of the distributed network for more eficient orchestration and automation
network serviccs. The SDN controller platforms that organizations use allow
communication between the now separated network planes.
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Software Defined Networks 1-9 SDN: Introduction

Software Defined Networking cnables the network administrators to deal with the data
in the network in a more efficient and innovative manner. By using SDN network
administrators have the ability to control the data flow as well as to alter the
characteristics of the switching devices (routing devices) in the network from a central
location with control application implemented as software modules without the need of
dealing with cach device individually.
This gives the network administrators the ability to change routing tables in network
routing devices. This gives an extra layer of control over the network data as the
administrator can assign high/low priority to certain data packets or allow/block certain
packets flowing through the network with different levels of control. As a result the
network traffic can be controlled in an efficient manner and hence can be used as a
mechanism for traffic load management in networks.
1.2.5 Challenges of Software-Defined Networking
1. Scalability : When the network scales up in terms of both size and diameter,
communication delays between the SDN controller and the network switches may
become high, thus affecting flow-setup latencies.
2. Flexibility and performance : Flexibility refers to the capability possessed by
networks to adjust to new and unprecedented features such as; applications and
network services. Performance here deals with speed at which network nodes at the
data plane process information from control plane.
3. Security : Various threat mitigation strategies would eventually arise even as the
potential for unauthorized access increases. The best solution is for organizations to
define an efficient high-level security policy to effectively attain network protection.
4. Interoperability : In today's multi-vendor environments, the limited interoperability
between SDN controller platforms is mainly due to a lack of open standards for inter
controller communications.

1.2.6 Why SDN

. Current network elements (router, swilches) are limited controllable and programmable.
The network nodes are closed and bound to specific hardware.
" Updating topology and routing table entries are complex tasks. No open standardized
interfuce to control and manage network hardware has been available at the beginning of
SDN.

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 SON: Introductior
Srtware Defred i e t s 1-10

without providing the ability for

Poters ard switches are regarded as closed source,
enhancerments, simplified external control, functional substitutions or
flexible functional
network evolution through new protocols.
separated from physical network
With SDN, your services arnd 2pplications are logically
hardware and connections.
bandwidth management, restoration
With SDN's central control and intelligence,
security and policies become highly optimized.
using software external to the physica
The ability to control network behavior
networks in support of new
networking devices gives an easy way to customize
Services.

SDN software can control hardware from disparate vendors that utilize open
" Intelligent
programmatic interfaces, such as OpenFlow.
?
Why is software-defined networking useful
Reasons are as follows :
resulting from the separation from
1. Ease of network control via irect programming
forwarding functions.
balancing to manage the traffic flow
2. Agility and the ability to dynamically use load increasing the efficiency of the
as needed and usage fluctuates. This reduces latency,
network
3. Greater granularity of control over Security.
4. Ease of configuration.
5. Simplified network design and operation through the use of open controllers rather
than vendor-specific devices and protocols.

1.2.7 SDN Operation

and s
" Software control program (controller) has an overview of the whole network
responsíble for the decision making, while the hardware (routers, switches etc.) s
s
simply responsible for forwarding packets into their destination as per the controller
instructions, typically a set of packet-handling rules.
SDN devices contain forwarding functionality for deciding what to do with eacl
incoming packet. The devices also contain the data which drives those forwardng
decisions. The data itself is actually represented by the flows defined by the contro
as depicted in the upper left portion of each device.

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Software Defined Networks 1-11 SDN: Introduction

" A network device is an aggregation of multiple resources such as ports, CPU, memory,
and queues. Examples of network devices include switches and routers. Each network
device has a presence in a forwarding planc and an operational planc.
" The operational plane is responsible for the operationalstate of the network device, for
instance, with respect to status of network ports and interfaces. Operational-plane
resources include, but are not limited to, memory, CPU, ports, interfaces and queues.
Fig. 1.2.2 shows SDN operation overview.
AppAppApp
Northbound
API Global network view

Daa
orwarding
fowarding
Controller
onwarding

Dat Dat
fonwarding Data
lonwarding foce
fonwarding

Openiiuw Southbound!
Data

API
forwarding

foewarding Data
forwardng
FOws
Flows
Data
lonwarding os forwarding

Dat
Fes onwarding Flows

Data Dat Data

bnardng rwardrg lonwarding owarding
Fows
sON devices
Data
lonwardng
Flow

lonwarding Data
orwardi
arding

Fig. 1.2.2 SDN operatlon overview

The SDN controller is responsible for abstracting the network of SDN devices it
controls and presenting an abstraction of these network resources to
the SDN
applications running above.
" The controller allows the SDN
application to define flows on devices and to help the
application to respond to packets which are forwarded to the controller by the
devices. SDN

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Software Defined Networks 1-12 SDN: Introduction
1.2.8 Advantages and Disadvantages of SDN
Advantages of SDN:
" It enables centralized management of networking devices.
SDN enables the rapid movement of workloads across a network.
Easily programmable : In SDN, control plane is easily programmable as it is separated
from the data plane.
" It offers flexibility, scalability and eficiency compared to traditional networking.
SDN allows centralized management of the entire network
Disadvantages of SDN:
Security is a big challenge in SDN.
Single point of failure.
Reconfiguring a SDN network is not a simple task since it involves lots of expenses.
1.3 SDN Data Plane, Control Plane and Application Plane
" In traditional network architecture, the control plane and data plane are integrated. Any
changes to the system are dependent upon configuring physical network devices, the
protocols and software they support.
Fig. 1.3.1 shows roles of thecontrol, management and data planes.
Data plane Control plane Management|
Unknown packets plane
control packets

Program Control and

Data in
forwarding
table
routing
protocols
SNMP

Configuration
Fowarding
table
Data out

Policy
Fig. 1.3.1 Roles of the control,
management and data planes
" In traditional network, data plane, control plane and
management plane are as tollows
1. SDN data plane
Ihe dala plane, also known as the forwarding plane, consists of a distributed set of
forwarding network elements in charge of forwarding packets.

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Software Defined Networks 1-13 SDN: Introduction

The data plane consists of the various ports that are used for the reception and
transmission of packets and a forwarding table with its associated logieThe data plane
assumes responsibility for packet buffering, packet scheduling, header modification and
fonwarding. )
If an aiving data packet's header information is found in the forwarding table it may be
subject to some header field modifications and then will be forwarded without any
intervention of the other two planes.
" Data plane is the network architecture layer that physically handles the traffic based on
the configurations supplied from the control plane. The data plane performs functions of
packet buffering, packet scheduling, header modification and forwarding.
Data plane : It performs packet streaming. Packet forward, filter, buffer, mark, rate
limit and measure packets are the other functions.
" The data plane parses packets headers, manages encapsulations, queuing and policing; it
deals with user traffic. When packets are destined to or originating from a router, they
do not go through its data plane, only its control plane.
" Only when packets are being sent through an intermediary router is when the
intermediary's data plane is in use. The management plane deals with administrative
traffic in order to manage network traffic.
2 SDN control plane

" Control plane refers to the network architecture component that defines the traffic
routing and network topology.
Control plane : It distributed algorithms and it maintains/performs track topology
changes, compute routes, install forwarding rules etc.
The control plane consists of a centralized software controller that is responsible for
handling communications between network applications and devices through open
interfaces.
" ts principal role is to keep current information in the forwarding table so that the data
plane can independently handle as high percentage of the traffic as possible.
The control plane is responsible for processing a number of different control protocols
that may affect the forwarding table, depending on the configuration and type of switch.
These control protocols are jointly responsible for managing the active topology ot the
network.

" The SDN control layer is commonly refered to as the network operating system as it
supports the network control logic and provides the application layer with an abstracted

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Sofware Defined Networks 1-14 SDN: Introduction
viey of the global network, which contains enough information to spccify policies whila
hiding all implementation details.
3. Management plane
" Network administrators configure and monitor the switch through this plane, which i
turn extracts information from or modifies data in the control and data planes as
appropriate.
" The network administrators use some form of network management system o
communicate to the management plane in a switch.
Management plane takes care of the wider network configuration, monitoring and
management processes across all layers of the network stack.
Management planes collect measurements and configure the equipment.
1.4 Two Marks Questions with Answers
Q.1 Define datagram.
Ans. : A datagram carries information sufficient for routing from the source to the destination
without the necessity of establishing a logical connection between the endpoints.
Q.2 Define packet.
Ans.: Apacket is a group of bits that includes data plus protocol control information.
0.3 What is software-defined networking?
Ans. : Software-Defined Networking (SDN) is an architecture designed to make a network
more flexible and easier to manage. SDN centralizes management by abstracting the control
plane from the data forwarding function in the discrete networking devices.
Q.4 What is control plane ?

Ans. : Control plane is a component for network in SDN which it can cary traffics and it can
focus on how individual package will interacts with its neighbours during state exchange.
5 What is SDN device ?

Ans. : An SDN device is composed of an API for communication with the controller, an
abstraction layer andapacket-processing function.
What is
south-bound Interface ?
Ans. : The southbound interface is a collection of drivers that handles communication to en
data-plane elements in the network.
0. What ls northbound Interface ?
Ans. : A northbound interface is an interface that allows a
particular component of a netwo
communicate with a higher-level component.
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Software Defined Networks 1 - 15 SDN: Introduction

Q.8 Define data plane.

Ans. : Data plane refers to the tasks that a networking device does to forward a message. The
data plane handles incoming datagrams through a series of link-level operations that collect the
datagram and perform basic checks.
Q.9 List the components of SDN.
Ans. : SDN components are : Data plane, control plan, soundbound interface, northbound
interface and application plane.
0.10 List the functions of control plane.
Ans. : Control plane functions are :

a) Topology discovery and maintenance

b) Packet route selection and instantiation
c) Path failover mechanism
0.11 What is network device?

Ans. : A network device is an entity that receives packets on its ports and perfoms one or more
network functions on them. Network devices can be implemented in hardware
or software and can be either a physical or virtual network element.

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