Computer Networks -CS6250 Exam 2025 Questions
and Answers
What is the control plane responsible for? - ✔✔Contains the logic that controls the
forwarding behaviors of routers such as routing protocols and network middlebox
What is the data plane responsible for? - ✔✔Performs the actual forwarding as dictated by
the control plane
Why are the data plane and control plane separate? - ✔✔Enables us to use higher-level
software programs for control, making it easier to debug and check the networks behavior
What is forwarding? - ✔✔When a router receives a packet, it must determine what output
link to send it through
What is routing? - ✔✔Determining the path from the sender to the receiver across the
network via routing algorithms
Where are routing algorithms processed? - ✔✔Control plane
Where are forwarding functions processed? - ✔✔Data plane
What are the main components of an SDN network? - ✔✔Infrastructure, controller, and
network-control applications
What is the SDN-controlled network (infrastructure) responsible for? - ✔✔Forwarding of
traffic in a network based on rules computed by the SDN control plane
,What is the SDN controller responsible for? - ✔✔Acts as an interface between the network
elements and network-control applications
What are network control applications responsible for? - ✔✔Programs that manage the
underlying network by collecting information about the network elements
In terms of the SDN architecture, what is flow-based forwarding? - ✔✔Rules for forwarding
packets can be computed based on any number of header field values in various layers - Differs
from the traditional approach where only the destination IP determines the forwarding of a
packet
What are the defining features of an SDN architecture - ✔✔Flow-based forwarding, network
control functions, programmable network
What are network control functions? - ✔✔Two components: Controller and network
applications
Controller maintains up-to-date network state information about the network devices and
elements (ex. Hosts, switches, links) and provides it to network-control applications
What is a programmable network? - ✔✔The "brain" of the SDN control plane; manages the
network
What plane is the SDN controller part of? - ✔✔Control plane
What are the layers of the SDN controller? - ✔✔Communication, network-wide state-
management, interface to the network-control application
In terms of the SDN controller, what does the communication layer do? - ✔✔Consists of a
protocol where the SDN controller and network controlled elements communicate
, What is the nickname for the communication layer of the SDN controller? - ✔✔Southbound
interface
In terms of the SDN controller, describe the network-wide state-management layer - ✔✔The
network-state that is maintained by the controllers
In terms of SDN, describe the network-control application layer - ✔✔This is how the SDN
controller interacts with network-control applications
What is another name for this layer? - ✔✔Northbound interface
What is the different between conventional and SDN? - ✔✔Conventional networks have
tightly coupled data and control plane
Software defined networks decouple the control plane from physical networking
What things should all SDN core controllers provide? - ✔✔Topology, statistics, notifications,
device management, shortest path forwarding, security mechanisms
What is a centralized controller? - ✔✔Typically has a single entity that manages all
forwarding devices in the network (a single point of failure)
What is a distributed controller? - ✔✔An entity that runs across multiple data centers
interconnected by a WAN
What is Open Networking Operating System (ONOS)? - ✔✔A distributed SDN control
platform
What is the goal of ONOS? - ✔✔Provide a global view of the network to the applications,
scale out performance and fault tolerance
and Answers
What is the control plane responsible for? - ✔✔Contains the logic that controls the
forwarding behaviors of routers such as routing protocols and network middlebox
What is the data plane responsible for? - ✔✔Performs the actual forwarding as dictated by
the control plane
Why are the data plane and control plane separate? - ✔✔Enables us to use higher-level
software programs for control, making it easier to debug and check the networks behavior
What is forwarding? - ✔✔When a router receives a packet, it must determine what output
link to send it through
What is routing? - ✔✔Determining the path from the sender to the receiver across the
network via routing algorithms
Where are routing algorithms processed? - ✔✔Control plane
Where are forwarding functions processed? - ✔✔Data plane
What are the main components of an SDN network? - ✔✔Infrastructure, controller, and
network-control applications
What is the SDN-controlled network (infrastructure) responsible for? - ✔✔Forwarding of
traffic in a network based on rules computed by the SDN control plane
,What is the SDN controller responsible for? - ✔✔Acts as an interface between the network
elements and network-control applications
What are network control applications responsible for? - ✔✔Programs that manage the
underlying network by collecting information about the network elements
In terms of the SDN architecture, what is flow-based forwarding? - ✔✔Rules for forwarding
packets can be computed based on any number of header field values in various layers - Differs
from the traditional approach where only the destination IP determines the forwarding of a
packet
What are the defining features of an SDN architecture - ✔✔Flow-based forwarding, network
control functions, programmable network
What are network control functions? - ✔✔Two components: Controller and network
applications
Controller maintains up-to-date network state information about the network devices and
elements (ex. Hosts, switches, links) and provides it to network-control applications
What is a programmable network? - ✔✔The "brain" of the SDN control plane; manages the
network
What plane is the SDN controller part of? - ✔✔Control plane
What are the layers of the SDN controller? - ✔✔Communication, network-wide state-
management, interface to the network-control application
In terms of the SDN controller, what does the communication layer do? - ✔✔Consists of a
protocol where the SDN controller and network controlled elements communicate
, What is the nickname for the communication layer of the SDN controller? - ✔✔Southbound
interface
In terms of the SDN controller, describe the network-wide state-management layer - ✔✔The
network-state that is maintained by the controllers
In terms of SDN, describe the network-control application layer - ✔✔This is how the SDN
controller interacts with network-control applications
What is another name for this layer? - ✔✔Northbound interface
What is the different between conventional and SDN? - ✔✔Conventional networks have
tightly coupled data and control plane
Software defined networks decouple the control plane from physical networking
What things should all SDN core controllers provide? - ✔✔Topology, statistics, notifications,
device management, shortest path forwarding, security mechanisms
What is a centralized controller? - ✔✔Typically has a single entity that manages all
forwarding devices in the network (a single point of failure)
What is a distributed controller? - ✔✔An entity that runs across multiple data centers
interconnected by a WAN
What is Open Networking Operating System (ONOS)? - ✔✔A distributed SDN control
platform
What is the goal of ONOS? - ✔✔Provide a global view of the network to the applications,
scale out performance and fault tolerance
