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CS6250 Module 7 Practice Questions and
Answers 2026
- What spurred the development of Software De- fined Networking (SDN)?
- 3 phases in the history of SDN
- Active Net- works
- Two types of pro- gramming mod- els in active net- working
- Pushes that en- couraged active networking
- 3 Major Contri- butions of Ac- tive Networking towards SDN
SDN was developed in order to make computer networks more programmable. With so many ditterent technologies and vendors for network devices, SDN helps redesign networks to make them more manageable.
- Active Networks
- Control and Data Plane Separation
- OpenFlow API and network operating systems
1990s-2000s
Active networking envisioned a programming interface that exposed network nodes and supported customization of functionalities for subsets of packets pass- ing through the network nodes.
- Capsule Model - code to execute was carried in-band in data packets
- Programmable router/switch model - code to execute was established by out-of-band mechanisms.
- Reduction in computation cost
- Advancement in programming languages and VM technology to protect active code.
- Advancement in code compilation
- Programmable functions in the network to lower the barrier to innovation.
- Network virtualization
- The vision of a unified architecture for middlebox orchestration
CS6250 Module 7 Practice Questions and
Answers 2026
- Biggest Downfall of Active Net- working
- Control and Data Plane Sepa- ration
- OpenFlow API and network op- erating systems
- How does an OpenFlow switch work?
- Function of the control pane and data plane
Too Ambitious
Since active networking was more involved in redesigning the architecture of networks, not as much emphasis was given to performance and security - which users were more concerned about
2001 to 2007
Packet forwarding was implemented directly in the hardware. This era tailored to administrators being able to control / manage routing decisions. Emphasized programmability in the control domain rather than the data domain.
2007 to 2010
The vision of fully programmable networks for research is realized, and then actually used by businesses / ISPs. Abstracted away the specifics of vendor software / proprietary products and allowed the entire network to be treated as one programmable entity.
Lead to the rise of network operating systems and distributed state management.
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 action associated with it and increments the counter.
The control plane contains the logic that implements the forwarding behavior of routers such as routing protocols and network middlebox configurations.
The data plane performs the actual forwarding as dictated by the control plane
- Why separate the Independent evolution and development - prior to their separation, any changes
control from the data plane?
to the control plane had to be met with upgrades to the hardware.
- 3 Main Compo- 1. SND-controlled network elements - infrastructure layer, responsible for forward- nents of SDN Net- ing traflc using rules computed by the SDN control plane. work
- 4 defining fea- tures in an SDN network
- 3 layers of SDN controller
- SDN controller - logically centralized entity that behaves as an interface between the network elements and the network-control applications.
- Network-control applications - programs that manage the underlying network by collecting information about the network elements with the help of the SDN controller
- Flow-base forwarding - rules for packets can be computed based on any number of header field values in various layers (transport, network, link).
- Separation of data and control planes
- Network control functions - controller maintains up-to-date network state in- formation and provides it to the network-control applications. This enables net- work-control applications to monitor and control network devices.
- Programmable network - enables the implementation of sophisticated routing applications to include network management, traflc engineering, security, au- tomation, analytics, etc.
- Communication layer - comms between the controller and the network ele- ments
- Network-wide state-management layer - stores information about the network state
- Interface to the network-control application layer - communication between controller and network-control applications
