CS6250 Exam 2 with complete answers (verified
answers) and complete solutions 2026.
L7: What spurred the development of Software Defined Networking
(SDN)?
> SDN arose to make CN more programmable
> Networks are complex/difficult to manage due to the diversity of
equipment on the network and proprietary technologies for the
equipment
> These made them highly complex, slow to innovate, and drove up the
costs of running a network.
SDN divides the network into two planes (separation of tasks):
1. control plane
2. data plane.
L7: What are the three phases in the history of SDN?
1. Active networks
2. Control and data plane separation
3. OpenFlow API and network operating systems
1|Page
,L7: Summarize each phase in the history of SDN.
1. Active networks
2. Control and data plane separation
3. OpenFlow API and network operating systems
Active networks
> Researchers wanted to test new ideas to improve network services.
This required standardization of new protocols by the IETF which was a
slow/frustrating process.
> More active networks which wanted to open up network control.
> Community belief: simplicity of the network core was vital to internet
success.
The pushes that encouraged active networking:
> Reduction in computation cost
> PL Advancement (like java)
> Advances in rapid code compilation and formal methods.
Active networking envisioned unified control that could replace
individually managing these boxes.
Active networks made three major contributions related to SDN:
> Programmable functions in the network to lower the barrier of
innovation
> Introduced the idea of using programmable networks to overcome the
slow speed of innovation in networking.
Active networking produced a framework that described a platform that
would support experimentation with different programming models. This
led to network visualization.
2|Page
,Active networking was more involved in redesigning the architecture of
networks, so not as much emphasis was given to performance and
security. Since there were no specific short-term problems that active
networks solved, it was harder to see widespread deployment.
The next efforts had a more focused scope and distinguished between
control and data planes. This difference made it easier to focus on
innovation in a specific plane and inflict widespread change.
Control and data plane separation
> Network operators were looking for better network-management
functions such as control over paths to deliver traffic.
> Identified that the challenge in network management depended on the
way existing routers and switches tightly integrated the control and data
planes.
> Efforts the separate the two began:
>> Higher link speeds in backbone networks led vendors to implement
packet forwarding directly in the hardware
>> ISPs found it hard to meet the increasing demands for greater
reliability and new services.
Two main innovations: Open interface between control and data planes
AND logically centralized control of the network
Differed from active networking, it:
> Focused on spurring innovation by/for network administrators rather
than end users/researchers.
> Emphasized programmability in the control domain rather than the
data domain.
> Worked to network-wide visibility rather than device
3|Page
, Attempts to separate control and data planes resulted in two concepts
used in further SDN design:
> Logically centralized control using an open interface to the data plane.
> Distributed state management - There was skepticism to moving away
from a simple network where all have a common view of the network
state to one where the router only had a local view of the outcome of
route-selection. This concept of separation of planes helped researchers
think clearly about distributed state management.
OpenFlow API and network operating systems
> OpenFlow was born out of interest in the idea of network
experimentation at scale, by researchers and funding agencies.
> OpenFlow built on the existing hardware and enabled more functions
than earlier route controllers. Enabled immediate deployment.
The basic working of an OpenFlow switch: Each switch contains a table
of packet-handling rules. Each rule has a pattern, list of actions, set of
counters and a priority. When an OpenFlow switch receives a packet, it
determines the highest priority matching rule, performs the associated
action and increments the counter.
OpenFlow was adopted in the industry, unlike its predecessors.
Companies started investing more in programmers to write control
programs, and less in proprietary switches that could not support new
features easily. This allowed many smaller players to become
competitive in the market by supporting capabilities like OpenFlow.
Key effects that OpenFlow had were:
Generalizing network devices and functions
Vision of a network operating systems
Distributed state management techniquesr
4|Page
answers) and complete solutions 2026.
L7: What spurred the development of Software Defined Networking
(SDN)?
> SDN arose to make CN more programmable
> Networks are complex/difficult to manage due to the diversity of
equipment on the network and proprietary technologies for the
equipment
> These made them highly complex, slow to innovate, and drove up the
costs of running a network.
SDN divides the network into two planes (separation of tasks):
1. control plane
2. data plane.
L7: What are the three phases in the history of SDN?
1. Active networks
2. Control and data plane separation
3. OpenFlow API and network operating systems
1|Page
,L7: Summarize each phase in the history of SDN.
1. Active networks
2. Control and data plane separation
3. OpenFlow API and network operating systems
Active networks
> Researchers wanted to test new ideas to improve network services.
This required standardization of new protocols by the IETF which was a
slow/frustrating process.
> More active networks which wanted to open up network control.
> Community belief: simplicity of the network core was vital to internet
success.
The pushes that encouraged active networking:
> Reduction in computation cost
> PL Advancement (like java)
> Advances in rapid code compilation and formal methods.
Active networking envisioned unified control that could replace
individually managing these boxes.
Active networks made three major contributions related to SDN:
> Programmable functions in the network to lower the barrier of
innovation
> Introduced the idea of using programmable networks to overcome the
slow speed of innovation in networking.
Active networking produced a framework that described a platform that
would support experimentation with different programming models. This
led to network visualization.
2|Page
,Active networking was more involved in redesigning the architecture of
networks, so not as much emphasis was given to performance and
security. Since there were no specific short-term problems that active
networks solved, it was harder to see widespread deployment.
The next efforts had a more focused scope and distinguished between
control and data planes. This difference made it easier to focus on
innovation in a specific plane and inflict widespread change.
Control and data plane separation
> Network operators were looking for better network-management
functions such as control over paths to deliver traffic.
> Identified that the challenge in network management depended on the
way existing routers and switches tightly integrated the control and data
planes.
> Efforts the separate the two began:
>> Higher link speeds in backbone networks led vendors to implement
packet forwarding directly in the hardware
>> ISPs found it hard to meet the increasing demands for greater
reliability and new services.
Two main innovations: Open interface between control and data planes
AND logically centralized control of the network
Differed from active networking, it:
> Focused on spurring innovation by/for network administrators rather
than end users/researchers.
> Emphasized programmability in the control domain rather than the
data domain.
> Worked to network-wide visibility rather than device
3|Page
, Attempts to separate control and data planes resulted in two concepts
used in further SDN design:
> Logically centralized control using an open interface to the data plane.
> Distributed state management - There was skepticism to moving away
from a simple network where all have a common view of the network
state to one where the router only had a local view of the outcome of
route-selection. This concept of separation of planes helped researchers
think clearly about distributed state management.
OpenFlow API and network operating systems
> OpenFlow was born out of interest in the idea of network
experimentation at scale, by researchers and funding agencies.
> OpenFlow built on the existing hardware and enabled more functions
than earlier route controllers. Enabled immediate deployment.
The basic working of an OpenFlow switch: Each switch contains a table
of packet-handling rules. Each rule has a pattern, list of actions, set of
counters and a priority. When an OpenFlow switch receives a packet, it
determines the highest priority matching rule, performs the associated
action and increments the counter.
OpenFlow was adopted in the industry, unlike its predecessors.
Companies started investing more in programmers to write control
programs, and less in proprietary switches that could not support new
features easily. This allowed many smaller players to become
competitive in the market by supporting capabilities like OpenFlow.
Key effects that OpenFlow had were:
Generalizing network devices and functions
Vision of a network operating systems
Distributed state management techniquesr
4|Page
