CS6250 Computer Networks Exam 2
Study Guide (2026–2027)
Section 1: Software-Defined Networking
(SDN) Fundamentals (Questions 1–25)
1. What are the two primary reasons computer networks became complex and difficult to
manage, leading to the development of SDN?
A. High bandwidth costs and slow routers
B. Diversity of network equipment and proprietary technology
C. DNS complexity and BGP convergence
D. IPv4 exhaustion and NAT proliferation
Correct Answer: B
Rationale: The two main drivers for SDN were (1) diversity of network equipment (routers,
switches, firewalls) using different protocols that made management difficult, and (2)
proprietary technology requiring equipment-specific configuration, which prevented
centralized management .
2. What is the simple core idea behind SDN that helps make networks more manageable?
A. Increasing router processing power
B. Separating the control plane and data plane
C. Eliminating all middleboxes
D. Centralizing all traffic through one router
Correct Answer: B
Rationale: SDN separates the control plane (routing decisions) from the data plane (packet
forwarding), allowing the control plane to be centralized in software controllers while data
plane devices focus solely on forwarding .
3. In traditional networking, how are the control plane and data plane related?
A. They are completely independent
B. They are closely coupled within each router
C. The data plane controls the control plane
D. They are separated by the SDN controller
Correct Answer: B
,Rationale: In traditional networks, routing algorithms (control plane) and forwarding
functions (data plane) are closely coupled. Each router runs routing algorithms to construct
its own forwarding table .
4. In the SDN approach, what is responsible for computing and distributing forwarding
tables?
A. Each individual router
B. The data plane switches
C. A remote SDN controller
D. End host applications
Correct Answer: C
Rationale: In SDN, a remote controller is responsible for computing and distributing
forwarding tables to the switches. The switches then consult these tables for forwarding
decisions .
5. Which of the following is NOT a defining feature of SDN architecture?
A. Separation of control and data planes
B. Centralized network control
C. Proprietary vendor-specific configuration
D. Programmable network functions
Correct Answer: C
Rationale: SDN aims to eliminate proprietary vendor-specific configuration by providing
open, programmable interfaces. The four defining features include control/data plane
separation, centralized control, programmable functions, and open interfaces .
6. What are the three phases in the history of SDN?
A. ARPANET, NSFNET, Internet2
B. Active networks, control/data plane separation, OpenFlow API and NOS
C. Routing, switching, SDN
D. IPv4, IPv6, SDN
Correct Answer: B
Rationale: The three phases of SDN history are: (1) Active networks, (2) Control and data
plane separation, and (3) OpenFlow API and network operating systems .
7. What was the primary goal of active networks?
A. To simplify the network core
B. To open up network control with APIs that support customization
, C. To eliminate all protocols
D. To centralize all routing decisions
Correct Answer: B
Rationale: Active networks aimed to open up network control with an API that exposes
resources and supports customization of functionalities for subsets of packets passing
through network nodes .
8. Why did active networks conflict with the end-to-end (E2E) principle?
A. They required customization at network nodes rather than simplicity at the core
B. They eliminated all network intelligence
C. They only worked with IPv6
D. They required all packets to be encrypted
Correct Answer: A
Rationale: Active networks required customization at network nodes, which conflicted with
the E2E principle that advocates for simplicity in the network core and intelligence at the
endpoints .
9. What were the two types of programming models in active networking?
A. Centralized and distributed
B. Capsule model and programmable router/switch model
C. Static and dynamic
D. In-band and out-of-band
Correct Answer: B
Rationale: The two models were: (1) Capsule model — code carried in-band in data packets,
and (2) Programmable router/switch model — code distribution via out-of-band
mechanisms with decision-making by the network operator .
10. Which plane are active networks primarily associated with?
A. Control plane
B. Data plane
C. Management plane
D. Application plane
Correct Answer: B
Rationale: Active networks are associated with the data plane, focusing on increasing
programmability at network nodes to customize packet processing .
11. What is the relationship between the SDN controller and the data plane switches?
Study Guide (2026–2027)
Section 1: Software-Defined Networking
(SDN) Fundamentals (Questions 1–25)
1. What are the two primary reasons computer networks became complex and difficult to
manage, leading to the development of SDN?
A. High bandwidth costs and slow routers
B. Diversity of network equipment and proprietary technology
C. DNS complexity and BGP convergence
D. IPv4 exhaustion and NAT proliferation
Correct Answer: B
Rationale: The two main drivers for SDN were (1) diversity of network equipment (routers,
switches, firewalls) using different protocols that made management difficult, and (2)
proprietary technology requiring equipment-specific configuration, which prevented
centralized management .
2. What is the simple core idea behind SDN that helps make networks more manageable?
A. Increasing router processing power
B. Separating the control plane and data plane
C. Eliminating all middleboxes
D. Centralizing all traffic through one router
Correct Answer: B
Rationale: SDN separates the control plane (routing decisions) from the data plane (packet
forwarding), allowing the control plane to be centralized in software controllers while data
plane devices focus solely on forwarding .
3. In traditional networking, how are the control plane and data plane related?
A. They are completely independent
B. They are closely coupled within each router
C. The data plane controls the control plane
D. They are separated by the SDN controller
Correct Answer: B
,Rationale: In traditional networks, routing algorithms (control plane) and forwarding
functions (data plane) are closely coupled. Each router runs routing algorithms to construct
its own forwarding table .
4. In the SDN approach, what is responsible for computing and distributing forwarding
tables?
A. Each individual router
B. The data plane switches
C. A remote SDN controller
D. End host applications
Correct Answer: C
Rationale: In SDN, a remote controller is responsible for computing and distributing
forwarding tables to the switches. The switches then consult these tables for forwarding
decisions .
5. Which of the following is NOT a defining feature of SDN architecture?
A. Separation of control and data planes
B. Centralized network control
C. Proprietary vendor-specific configuration
D. Programmable network functions
Correct Answer: C
Rationale: SDN aims to eliminate proprietary vendor-specific configuration by providing
open, programmable interfaces. The four defining features include control/data plane
separation, centralized control, programmable functions, and open interfaces .
6. What are the three phases in the history of SDN?
A. ARPANET, NSFNET, Internet2
B. Active networks, control/data plane separation, OpenFlow API and NOS
C. Routing, switching, SDN
D. IPv4, IPv6, SDN
Correct Answer: B
Rationale: The three phases of SDN history are: (1) Active networks, (2) Control and data
plane separation, and (3) OpenFlow API and network operating systems .
7. What was the primary goal of active networks?
A. To simplify the network core
B. To open up network control with APIs that support customization
, C. To eliminate all protocols
D. To centralize all routing decisions
Correct Answer: B
Rationale: Active networks aimed to open up network control with an API that exposes
resources and supports customization of functionalities for subsets of packets passing
through network nodes .
8. Why did active networks conflict with the end-to-end (E2E) principle?
A. They required customization at network nodes rather than simplicity at the core
B. They eliminated all network intelligence
C. They only worked with IPv6
D. They required all packets to be encrypted
Correct Answer: A
Rationale: Active networks required customization at network nodes, which conflicted with
the E2E principle that advocates for simplicity in the network core and intelligence at the
endpoints .
9. What were the two types of programming models in active networking?
A. Centralized and distributed
B. Capsule model and programmable router/switch model
C. Static and dynamic
D. In-band and out-of-band
Correct Answer: B
Rationale: The two models were: (1) Capsule model — code carried in-band in data packets,
and (2) Programmable router/switch model — code distribution via out-of-band
mechanisms with decision-making by the network operator .
10. Which plane are active networks primarily associated with?
A. Control plane
B. Data plane
C. Management plane
D. Application plane
Correct Answer: B
Rationale: Active networks are associated with the data plane, focusing on increasing
programmability at network nodes to customize packet processing .
11. What is the relationship between the SDN controller and the data plane switches?
