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CS6250 COMPUTER NETWORK EXAM 2 ACTUAL
EXAM 2026/2027 Expert Certified Questions and Answers |
Already Graded A+ Complete Questions and Answers
Expert Verified Pass Guaranteed - A+ Graded
SECTION 1: SOFTWARE-DEFINED NETWORKING (SDN)
Q1: In an OpenFlow-based SDN network, a switch receives a packet for which it has no
matching flow table entry. Which of the following actions will occur?
A. The switch drops the packet immediately to prevent forwarding loops
B. The switch forwards the packet using traditional MAC learning
C. The switch encapsulates the packet and sends it to the controller
D. The switch floods the packet out all ports except the incoming port
Correct Answer: C
Rationale: In OpenFlow, when a packet does not match any flow table entry (table-miss), the
switch's default behavior is to send the packet to the controller for processing. [CORRECT]
Option C is correct because the controller can then decide how to handle the packet and
potentially install new flow entries. Option A is incorrect because dropping is only one possible
table-miss action, not the default. Option B is incorrect because SDN decouples control and data
planes; traditional MAC learning occurs in the control plane, not autonomously on the switch.
Option D describes traditional Ethernet switch behavior, not OpenFlow SDN.
Q2: Which of the following best describes the "southbound" interface in an SDN architecture?
A. The API used by network applications to communicate with the SDN controller
B. The interface between the SDN controller and the network devices (e.g., OpenFlow)
C. The protocol used for east-west communication between distributed controllers
D. The management interface for network administrators to configure the controller
Correct Answer: B
Rationale: The southbound interface is the interface between the SDN controller and the network
infrastructure devices (data plane). [CORRECT] Option B correctly identifies this definition
(e.g., OpenFlow). Option A describes the northbound interface. Option C refers to east-
,2
westbound interfaces used for controller synchronization. Option D refers to management
interfaces (often CLI or GUI), not the architectural southbound interface.
Q3: In a network utilizing ONOS (Open Network Operating System), what is the primary
function of the "Global Graph View"?
A. It stores packet captures for forensic analysis
B. It provides a synchronized, consistent view of the entire network topology to all controller
instances
C. It acts as a local cache for flow rules on individual switches to reduce latency
D. It encrypts control plane traffic between the controller and switches
Correct Answer: B
Rationale: ONOS provides a global view of the network topology, abstracting the underlying
infrastructure. [CORRECT] Option B is correct because this global view is essential for
centralized control and is synchronized across distributed controller instances for high
availability. Option A is a function of monitoring tools, not the core Graph View. Option C refers
to hardware tables or switch-level caching. Option D is a security function, typically handled by
TLS/SSL channels.
Q4: A network engineer is implementing a "Proactive" SDN flow installation strategy. How does
this differ from a "Reactive" strategy?
A. Proactive installs rules in response to incoming packets; Reactive installs rules before traffic
flows
B. Proactive installs rules before traffic flows (e.g., at initialization); Reactive installs rules in
response to incoming packets
C. Proactive relies on traditional routing protocols; Reactive uses OpenFlow exclusively
D. Proactive is used for TCP traffic; Reactive is used for UDP traffic
Correct Answer: B
Rationale: Proactive flow installation involves the controller pre-populating flow tables before
traffic arrives, reducing latency for the first packet. [CORRECT] Option B is the correct
definition. Option A reverses the definitions. Option C is incorrect because proactive SDN still
uses OpenFlow or similar protocols, not traditional routing protocols on the switch. Option D has
no correlation with transport layer protocols.
,3
Q5: What is the primary disadvantage of a "Reactive" SDN flow installation approach in a high-
traffic data center environment?
A. It consumes excessive switch TCAM space due to storing all possible flows
B. It introduces latency for the first packet of every new flow due to controller communication
C. It prevents the use of wildcard flow entries
D. It requires the controller to be offline during rule installation
Correct Answer: B
Rationale: In reactive mode, the first packet of a flow (packet-in) triggers a communication
exchange between the switch and the controller to install the rule. [CORRECT] Option B is
correct because this "first packet latency" can be detrimental in high-performance environments.
Option A is more associated with proactive mode storing specific rules or reactive mode with
poor flow eviction policies, but the primary disadvantage is the latency bottleneck at the
controller. Option C is incorrect; wildcard entries can be used in both. Option D is false; the
controller must be online.
Q6: Which OpenFlow instruction causes a packet to be immediately removed from the current
processing pipeline and sent to the specified table?
A. Apply-Actions
B. Write-Actions
C. Goto-Table
D. Meter
Correct Answer: C
Rationale: The Goto-Table instruction is used in OpenFlow to direct the packet processing to a
subsequent flow table in the pipeline. [CORRECT] Option C is correct. Apply-Actions (A)
executes actions immediately but continues processing in the same table. Write-Actions (B)
accumulates actions to be executed at the end of the pipeline. Meter (D) is used for QoS/rate
limiting, not flow control logic.
Q7: In the context of SDN controllers like OpenDaylight, what is the function of MD-SAL
(Model-Driven Service Abstraction Layer)?
, 4
A. To provide a proprietary interface for Cisco devices only
B. To decouple applications from the specific details of southbound protocols and device
configurations
C. To manage the physical cabling of the data center
D. To act as a replacement for the OpenFlow protocol
Correct Answer: B
Rationale: MD-SAL provides a unified abstraction layer that allows applications to interact with
the network without needing to know the specifics of underlying devices or protocols
(NETCONF, OpenFlow, etc.). [CORRECT] Option B is correct. Option A is incorrect; it is
designed for multi-vendor interoperability. Option C is physical layer management. Option D is
incorrect; SAL works with protocols like OpenFlow, it doesn't replace them.
Q8: Consider an SDN architecture with a centralized controller. If the controller fails, what is the
immediate impact on a switch handling an established TCP flow with specific flow rules already
installed?
A. The switch immediately drops all packets for that TCP flow
B. The switch continues to forward packets for that flow according to the existing rules until the
idle timer expires
C. The switch sends an ARP request to find the controller backup
D. The switch reverts to traditional Layer 3 routing protocols
Correct Answer: B
Rationale: In SDN, the data plane (switches) is separate from the control plane (controller). Once
flow rules are installed, the switch can process packets independently of the controller.
[CORRECT] Option B is correct because the switch operates autonomously based on its current
table entries. Option A is false if the rules exist. Option C is incorrect; ARP is for IP resolution,
not controller discovery (typically done via IP/TCP connection). Option D is false; switches do
not automatically revert to traditional protocols unless specifically programmed to do so.
Q9: A network administrator wants to implement "Network Slicing" using SDN. Which feature
allows the administrator to isolate traffic for different applications on the same physical
infrastructure?
A. Link Aggregation
CS6250 COMPUTER NETWORK EXAM 2 ACTUAL
EXAM 2026/2027 Expert Certified Questions and Answers |
Already Graded A+ Complete Questions and Answers
Expert Verified Pass Guaranteed - A+ Graded
SECTION 1: SOFTWARE-DEFINED NETWORKING (SDN)
Q1: In an OpenFlow-based SDN network, a switch receives a packet for which it has no
matching flow table entry. Which of the following actions will occur?
A. The switch drops the packet immediately to prevent forwarding loops
B. The switch forwards the packet using traditional MAC learning
C. The switch encapsulates the packet and sends it to the controller
D. The switch floods the packet out all ports except the incoming port
Correct Answer: C
Rationale: In OpenFlow, when a packet does not match any flow table entry (table-miss), the
switch's default behavior is to send the packet to the controller for processing. [CORRECT]
Option C is correct because the controller can then decide how to handle the packet and
potentially install new flow entries. Option A is incorrect because dropping is only one possible
table-miss action, not the default. Option B is incorrect because SDN decouples control and data
planes; traditional MAC learning occurs in the control plane, not autonomously on the switch.
Option D describes traditional Ethernet switch behavior, not OpenFlow SDN.
Q2: Which of the following best describes the "southbound" interface in an SDN architecture?
A. The API used by network applications to communicate with the SDN controller
B. The interface between the SDN controller and the network devices (e.g., OpenFlow)
C. The protocol used for east-west communication between distributed controllers
D. The management interface for network administrators to configure the controller
Correct Answer: B
Rationale: The southbound interface is the interface between the SDN controller and the network
infrastructure devices (data plane). [CORRECT] Option B correctly identifies this definition
(e.g., OpenFlow). Option A describes the northbound interface. Option C refers to east-
,2
westbound interfaces used for controller synchronization. Option D refers to management
interfaces (often CLI or GUI), not the architectural southbound interface.
Q3: In a network utilizing ONOS (Open Network Operating System), what is the primary
function of the "Global Graph View"?
A. It stores packet captures for forensic analysis
B. It provides a synchronized, consistent view of the entire network topology to all controller
instances
C. It acts as a local cache for flow rules on individual switches to reduce latency
D. It encrypts control plane traffic between the controller and switches
Correct Answer: B
Rationale: ONOS provides a global view of the network topology, abstracting the underlying
infrastructure. [CORRECT] Option B is correct because this global view is essential for
centralized control and is synchronized across distributed controller instances for high
availability. Option A is a function of monitoring tools, not the core Graph View. Option C refers
to hardware tables or switch-level caching. Option D is a security function, typically handled by
TLS/SSL channels.
Q4: A network engineer is implementing a "Proactive" SDN flow installation strategy. How does
this differ from a "Reactive" strategy?
A. Proactive installs rules in response to incoming packets; Reactive installs rules before traffic
flows
B. Proactive installs rules before traffic flows (e.g., at initialization); Reactive installs rules in
response to incoming packets
C. Proactive relies on traditional routing protocols; Reactive uses OpenFlow exclusively
D. Proactive is used for TCP traffic; Reactive is used for UDP traffic
Correct Answer: B
Rationale: Proactive flow installation involves the controller pre-populating flow tables before
traffic arrives, reducing latency for the first packet. [CORRECT] Option B is the correct
definition. Option A reverses the definitions. Option C is incorrect because proactive SDN still
uses OpenFlow or similar protocols, not traditional routing protocols on the switch. Option D has
no correlation with transport layer protocols.
,3
Q5: What is the primary disadvantage of a "Reactive" SDN flow installation approach in a high-
traffic data center environment?
A. It consumes excessive switch TCAM space due to storing all possible flows
B. It introduces latency for the first packet of every new flow due to controller communication
C. It prevents the use of wildcard flow entries
D. It requires the controller to be offline during rule installation
Correct Answer: B
Rationale: In reactive mode, the first packet of a flow (packet-in) triggers a communication
exchange between the switch and the controller to install the rule. [CORRECT] Option B is
correct because this "first packet latency" can be detrimental in high-performance environments.
Option A is more associated with proactive mode storing specific rules or reactive mode with
poor flow eviction policies, but the primary disadvantage is the latency bottleneck at the
controller. Option C is incorrect; wildcard entries can be used in both. Option D is false; the
controller must be online.
Q6: Which OpenFlow instruction causes a packet to be immediately removed from the current
processing pipeline and sent to the specified table?
A. Apply-Actions
B. Write-Actions
C. Goto-Table
D. Meter
Correct Answer: C
Rationale: The Goto-Table instruction is used in OpenFlow to direct the packet processing to a
subsequent flow table in the pipeline. [CORRECT] Option C is correct. Apply-Actions (A)
executes actions immediately but continues processing in the same table. Write-Actions (B)
accumulates actions to be executed at the end of the pipeline. Meter (D) is used for QoS/rate
limiting, not flow control logic.
Q7: In the context of SDN controllers like OpenDaylight, what is the function of MD-SAL
(Model-Driven Service Abstraction Layer)?
, 4
A. To provide a proprietary interface for Cisco devices only
B. To decouple applications from the specific details of southbound protocols and device
configurations
C. To manage the physical cabling of the data center
D. To act as a replacement for the OpenFlow protocol
Correct Answer: B
Rationale: MD-SAL provides a unified abstraction layer that allows applications to interact with
the network without needing to know the specifics of underlying devices or protocols
(NETCONF, OpenFlow, etc.). [CORRECT] Option B is correct. Option A is incorrect; it is
designed for multi-vendor interoperability. Option C is physical layer management. Option D is
incorrect; SAL works with protocols like OpenFlow, it doesn't replace them.
Q8: Consider an SDN architecture with a centralized controller. If the controller fails, what is the
immediate impact on a switch handling an established TCP flow with specific flow rules already
installed?
A. The switch immediately drops all packets for that TCP flow
B. The switch continues to forward packets for that flow according to the existing rules until the
idle timer expires
C. The switch sends an ARP request to find the controller backup
D. The switch reverts to traditional Layer 3 routing protocols
Correct Answer: B
Rationale: In SDN, the data plane (switches) is separate from the control plane (controller). Once
flow rules are installed, the switch can process packets independently of the controller.
[CORRECT] Option B is correct because the switch operates autonomously based on its current
table entries. Option A is false if the rules exist. Option C is incorrect; ARP is for IP resolution,
not controller discovery (typically done via IP/TCP connection). Option D is false; switches do
not automatically revert to traditional protocols unless specifically programmed to do so.
Q9: A network administrator wants to implement "Network Slicing" using SDN. Which feature
allows the administrator to isolate traffic for different applications on the same physical
infrastructure?
A. Link Aggregation
