WGU D415 Software Defined Networking SDN Objective
Assessment Actual Exam 2026/2027 | Complete Review
with Detailed Rationales | Pass Guaranteed – A+ Graded
Section 1: SDN Architecture & Core Concepts (12 Questions)
Q1: Which plane in traditional networking is responsible for populating the Forwarding
Information Base (FIB) through routing protocols such as OSPF and BGP?
A. Data plane
B. Control plane
C. Management plane
D. Application plane
Correct Answer: B
Rationale: The control plane makes forwarding decisions, runs routing protocols (OSPF,
BGP, IS-IS), computes routing tables, and populates the FIB. The data plane forwards
packets based on the FIB. The management plane handles configuration and
monitoring.
Q2: In SDN architecture, which layer contains the physical switches and routers that
forward packets based on flow table entries?
A. Application layer
B. Control layer
,C. Infrastructure layer
D. Orchestration layer
Correct Answer: C
Rationale: The infrastructure layer (data plane) contains forwarding devices such as
switches and routers that perform packet forwarding based on instructions from the
controller. The control layer contains the SDN controller, and the application layer hosts
network applications.
Q3: A network administrator migrates from a traditional network to SDN. Which benefit
results from separating the control plane from the data plane?
A. Switches must run more complex routing protocols locally
B. Centralized visibility and simplified network management
C. Increased dependence on vendor-specific CLI configurations
D. Elimination of all network traffic forwarding
Correct Answer: B
Rationale: Separation of the control and data planes enables centralized visibility,
simplified management, network programmability, automation, and consistent policy
enforcement across the network. It reduces complexity on individual switches and
reduces vendor lock-in.
Q4: Which interface in SDN architecture allows communication between the SDN
controller and network applications such as load balancers or firewalls?
,A. Southbound interface
B. East-west interface
C. Northbound interface
D. Management interface
Correct Answer: C
Rationale: The northbound interface (NBI) connects the controller to applications and
services. Southbound interfaces connect controllers to forwarding devices. East-west
interfaces facilitate communication between distributed controllers.
Q5: In a hybrid SDN deployment, how does the switch handle traffic that does not match
any OpenFlow flow entry?
A. It is always dropped
B. It is always sent to the controller
C. It may fall back to traditional forwarding (e.g., normal L2/L3 processing)
D. It triggers a controller cluster election
Correct Answer: C
Rationale: Hybrid SDN allows traditional protocols (STP, OSPF, BGP) to coexist with
OpenFlow. If no OpenFlow match exists, the switch can fall back to traditional
forwarding, providing a gradual migration path and ensuring connectivity for unhandled
flows.
, Q6: Which memory type do OpenFlow switches typically use to perform high-speed
lookups of flow table entries?
A. DRAM
B. TCAM (Ternary Content-Addressable Memory)
C. Flash memory
D. SRAM
Correct Answer: B
Rationale: TCAM enables high-speed, parallel matching of packets against flow table
entries using ternary logic (0, 1, don't care). It is essential for line-rate forwarding in
hardware switches but is limited in size and more expensive than standard memory.
Q7: A company adopts network programmability to automate configuration changes
across 500 devices. Which approach best describes "network-centric" management
compared to "device-centric" management?
A. Administrators log into each device individually via SSH
B. A central system manages the entire network as a unified entity through policies and
APIs
C. Each device independently downloads configurations from a TFTP server
D. SNMP traps are used exclusively for device-level monitoring
Correct Answer: B
Assessment Actual Exam 2026/2027 | Complete Review
with Detailed Rationales | Pass Guaranteed – A+ Graded
Section 1: SDN Architecture & Core Concepts (12 Questions)
Q1: Which plane in traditional networking is responsible for populating the Forwarding
Information Base (FIB) through routing protocols such as OSPF and BGP?
A. Data plane
B. Control plane
C. Management plane
D. Application plane
Correct Answer: B
Rationale: The control plane makes forwarding decisions, runs routing protocols (OSPF,
BGP, IS-IS), computes routing tables, and populates the FIB. The data plane forwards
packets based on the FIB. The management plane handles configuration and
monitoring.
Q2: In SDN architecture, which layer contains the physical switches and routers that
forward packets based on flow table entries?
A. Application layer
B. Control layer
,C. Infrastructure layer
D. Orchestration layer
Correct Answer: C
Rationale: The infrastructure layer (data plane) contains forwarding devices such as
switches and routers that perform packet forwarding based on instructions from the
controller. The control layer contains the SDN controller, and the application layer hosts
network applications.
Q3: A network administrator migrates from a traditional network to SDN. Which benefit
results from separating the control plane from the data plane?
A. Switches must run more complex routing protocols locally
B. Centralized visibility and simplified network management
C. Increased dependence on vendor-specific CLI configurations
D. Elimination of all network traffic forwarding
Correct Answer: B
Rationale: Separation of the control and data planes enables centralized visibility,
simplified management, network programmability, automation, and consistent policy
enforcement across the network. It reduces complexity on individual switches and
reduces vendor lock-in.
Q4: Which interface in SDN architecture allows communication between the SDN
controller and network applications such as load balancers or firewalls?
,A. Southbound interface
B. East-west interface
C. Northbound interface
D. Management interface
Correct Answer: C
Rationale: The northbound interface (NBI) connects the controller to applications and
services. Southbound interfaces connect controllers to forwarding devices. East-west
interfaces facilitate communication between distributed controllers.
Q5: In a hybrid SDN deployment, how does the switch handle traffic that does not match
any OpenFlow flow entry?
A. It is always dropped
B. It is always sent to the controller
C. It may fall back to traditional forwarding (e.g., normal L2/L3 processing)
D. It triggers a controller cluster election
Correct Answer: C
Rationale: Hybrid SDN allows traditional protocols (STP, OSPF, BGP) to coexist with
OpenFlow. If no OpenFlow match exists, the switch can fall back to traditional
forwarding, providing a gradual migration path and ensuring connectivity for unhandled
flows.
, Q6: Which memory type do OpenFlow switches typically use to perform high-speed
lookups of flow table entries?
A. DRAM
B. TCAM (Ternary Content-Addressable Memory)
C. Flash memory
D. SRAM
Correct Answer: B
Rationale: TCAM enables high-speed, parallel matching of packets against flow table
entries using ternary logic (0, 1, don't care). It is essential for line-rate forwarding in
hardware switches but is limited in size and more expensive than standard memory.
Q7: A company adopts network programmability to automate configuration changes
across 500 devices. Which approach best describes "network-centric" management
compared to "device-centric" management?
A. Administrators log into each device individually via SSH
B. A central system manages the entire network as a unified entity through policies and
APIs
C. Each device independently downloads configurations from a TFTP server
D. SNMP traps are used exclusively for device-level monitoring
Correct Answer: B
