CS 6250 COMPREHENSIVE ANSWERS AND
QUESTIONS SET A+
✔✔What are Network-Control applications? - ✔✔- PROGRAMMABLE applications
- programs that MANAGE underlying network by monitoring/controlling info about
network elements with the help of the SDN controller
- control plane
(7)
✔✔What are 4 defining features in SDN architecture? - ✔✔1. flow based forwarding
2. separation of control and data plane
3. network control functions
4. a programmable network
(7)
✔✔What is flow-based forwarding with SDN? What is the limit on header field values?
How is it different from the traditional approach? How many header fields does openflow
SDN allow? - ✔✔Rules for forwarding packets in SDN switches are computed based on
headers from various layers
ANY number of header field values is allowed in SDN
differs because in traditional, ONLY the destination IP determines forwarding of packet
Openflow SDN allows up to 11 fields
(7)
✔✔What is separation of control plane and data plane in SDN architecture involve
regarding switches and rules? - ✔✔SDN switches execute rules in flow tables
,Rules are managed by software on separate servers
(7)
✔✔What are the differences between control and network applications regarding
network control functions? - ✔✔- controller maintains network info about devices and
sends into to applications (serving as an interface)
- network-control applications monitor and control the network devices (Switches,
routers, etc)
(7)
✔✔What is the brain of the control plane with SDN? - ✔✔Network-control applications
✔✔Where would traffic engineering, automation, etc. take place with SDN? - ✔✔These
are the programmable network control applications on the control plane
(7)
✔✔What is the SDN controller? - ✔✔Interface between network elements and network-
control applications on the control plane
(7)
✔✔What are the 3 layers of the SDN controller? - ✔✔1. communication layer
-communicate between controller and network elements
2. network wide state-management layer
- stores info on network state
- distributed
3. interface to network-control application layer
- communicate between controller and applications
(7)
✔✔What is the communication layer of an SDN controller? - ✔✔- Consists of protocol
through which SDN CONTROLLER and NETWORK CONTROLLED ELEMENTS
communicate
- elements send view of network state such as a device joining, a heartbeat, etc.
- Southbound interface is the communication between controller and the devices
(7)
✔✔What is the southbound interface? - ✔✔communication protocol between controller
and controlled devices
(7)
,✔✔What in SDN is openflow an example of? - ✔✔the southbound
interface/communication layer of the controller
(7)
✔✔What is the network-wide state-management layer? - ✔✔- stores network state that
is maintained by controller
- info about state of hosts, and other controlled devices/elements
- includes copies of flow tables
- this info is needed to configure flow tables
(7)
✔✔Why does network state info need to be strored by controller? - ✔✔In order to
configure flow tables
(7)
✔✔What is the interface to the network control application layer? How do apps interact
with it? - ✔✔- Northbound interface
- How SDN controller interacts with network-control applications
- apps read/write network state and flow tables in controller's state management layer
- controller notifies apps of changes in network state based on notifications from the
devices
- apps take actions based on events
(7)
✔✔What is the northbound interface? - ✔✔- controller to applications protocol
(7)
✔✔Is the SDN controller implemented centralized or distributed? - ✔✔DISTRIBUTED
SERVERS - highly scalable services
(7)
✔✔Is SDN controller have fault tolerance? Efficiency? Availability? Synchronization?
Why?? - ✔✔Yes to all EXCEPT synchronization b/c of distributed servers
(7)
✔✔What are 2 challenges that became more pronounced as IP networks grew in
adoption worldwide? - ✔✔1. handling growing complexity and dynamic nature of
networks
, - a policy requires changes t EVERY device
2. tightly coupled architecture
- traditionally control/data plane were together, which is not flexible
(8)
✔✔What is software defined networking? - ✔✔- attempt to overcome limits of legacy IP
networking
- separate control logic from data plane
- data plane switches do forwarding, control logic is in logically centralized controller
(8)
✔✔What is the physical and logical location of control plane? - ✔✔PHYSICALLY
DISTRIBUTED and LOGICALLY CENTRALIZED
(8)
✔✔Do SDNs have logically distributed controller? - ✔✔No, logically CENTRALIZED
(8)
✔✔Do SDNS have a physically centralized control plane? - ✔✔No, physically
DISTRIBUTED
(8)
✔✔How is separation between control plane and data plane achieved? -
✔✔Programming interface/API between controller apps and switches/devices, like
OpenFlow API
(8)
✔✔What are the 3 planes of functionality of SDNs? - ✔✔- Data plane (EXECUTE
network policy, like forwarding)
- Control Plane (ENFORCE network policy, like path and protocol determination)
- Management Plane (DEFINE network policy, like monitoring and configuring the
control functionality - end users program here)
(8)
✔✔What were middleboxes traditionally used for? - ✔✔- Avoid modifying all control
plane devices when new feature is introduced
- Equipment through which features like firewalls and LOAD BALANCERS were
introduced
(8)
QUESTIONS SET A+
✔✔What are Network-Control applications? - ✔✔- PROGRAMMABLE applications
- programs that MANAGE underlying network by monitoring/controlling info about
network elements with the help of the SDN controller
- control plane
(7)
✔✔What are 4 defining features in SDN architecture? - ✔✔1. flow based forwarding
2. separation of control and data plane
3. network control functions
4. a programmable network
(7)
✔✔What is flow-based forwarding with SDN? What is the limit on header field values?
How is it different from the traditional approach? How many header fields does openflow
SDN allow? - ✔✔Rules for forwarding packets in SDN switches are computed based on
headers from various layers
ANY number of header field values is allowed in SDN
differs because in traditional, ONLY the destination IP determines forwarding of packet
Openflow SDN allows up to 11 fields
(7)
✔✔What is separation of control plane and data plane in SDN architecture involve
regarding switches and rules? - ✔✔SDN switches execute rules in flow tables
,Rules are managed by software on separate servers
(7)
✔✔What are the differences between control and network applications regarding
network control functions? - ✔✔- controller maintains network info about devices and
sends into to applications (serving as an interface)
- network-control applications monitor and control the network devices (Switches,
routers, etc)
(7)
✔✔What is the brain of the control plane with SDN? - ✔✔Network-control applications
✔✔Where would traffic engineering, automation, etc. take place with SDN? - ✔✔These
are the programmable network control applications on the control plane
(7)
✔✔What is the SDN controller? - ✔✔Interface between network elements and network-
control applications on the control plane
(7)
✔✔What are the 3 layers of the SDN controller? - ✔✔1. communication layer
-communicate between controller and network elements
2. network wide state-management layer
- stores info on network state
- distributed
3. interface to network-control application layer
- communicate between controller and applications
(7)
✔✔What is the communication layer of an SDN controller? - ✔✔- Consists of protocol
through which SDN CONTROLLER and NETWORK CONTROLLED ELEMENTS
communicate
- elements send view of network state such as a device joining, a heartbeat, etc.
- Southbound interface is the communication between controller and the devices
(7)
✔✔What is the southbound interface? - ✔✔communication protocol between controller
and controlled devices
(7)
,✔✔What in SDN is openflow an example of? - ✔✔the southbound
interface/communication layer of the controller
(7)
✔✔What is the network-wide state-management layer? - ✔✔- stores network state that
is maintained by controller
- info about state of hosts, and other controlled devices/elements
- includes copies of flow tables
- this info is needed to configure flow tables
(7)
✔✔Why does network state info need to be strored by controller? - ✔✔In order to
configure flow tables
(7)
✔✔What is the interface to the network control application layer? How do apps interact
with it? - ✔✔- Northbound interface
- How SDN controller interacts with network-control applications
- apps read/write network state and flow tables in controller's state management layer
- controller notifies apps of changes in network state based on notifications from the
devices
- apps take actions based on events
(7)
✔✔What is the northbound interface? - ✔✔- controller to applications protocol
(7)
✔✔Is the SDN controller implemented centralized or distributed? - ✔✔DISTRIBUTED
SERVERS - highly scalable services
(7)
✔✔Is SDN controller have fault tolerance? Efficiency? Availability? Synchronization?
Why?? - ✔✔Yes to all EXCEPT synchronization b/c of distributed servers
(7)
✔✔What are 2 challenges that became more pronounced as IP networks grew in
adoption worldwide? - ✔✔1. handling growing complexity and dynamic nature of
networks
, - a policy requires changes t EVERY device
2. tightly coupled architecture
- traditionally control/data plane were together, which is not flexible
(8)
✔✔What is software defined networking? - ✔✔- attempt to overcome limits of legacy IP
networking
- separate control logic from data plane
- data plane switches do forwarding, control logic is in logically centralized controller
(8)
✔✔What is the physical and logical location of control plane? - ✔✔PHYSICALLY
DISTRIBUTED and LOGICALLY CENTRALIZED
(8)
✔✔Do SDNs have logically distributed controller? - ✔✔No, logically CENTRALIZED
(8)
✔✔Do SDNS have a physically centralized control plane? - ✔✔No, physically
DISTRIBUTED
(8)
✔✔How is separation between control plane and data plane achieved? -
✔✔Programming interface/API between controller apps and switches/devices, like
OpenFlow API
(8)
✔✔What are the 3 planes of functionality of SDNs? - ✔✔- Data plane (EXECUTE
network policy, like forwarding)
- Control Plane (ENFORCE network policy, like path and protocol determination)
- Management Plane (DEFINE network policy, like monitoring and configuring the
control functionality - end users program here)
(8)
✔✔What were middleboxes traditionally used for? - ✔✔- Avoid modifying all control
plane devices when new feature is introduced
- Equipment through which features like firewalls and LOAD BALANCERS were
introduced
(8)
