Exam 2: Lesson 7 Flashcards
Lesson 7 (T/F):
A few of the main reasons that SDN arose are: a diversity of different network equipment (eg routers, switches, firewalls, etc.) using different protocols that made managing the network difficult, and second a lack of a central platform to control network equipment?
True
Lesson 7 (T/F):
The main idea behind SDNs is to divide tasks into smaller functions so the code is more modular and easy to manage.
True
Lesson 7 (T/F):
With SDNs the control plane and data plane have independent evolution and development.
True
- In the traditional approach, routers are responsible for both routing and forwarding functionalities. This meant that a change to either of the functions would require an upgrade of hardware.
- In this new approach, routers only focus on forwarding. Thus, innovation in this design can proceed independently of other routing considerations. Similarly, improvement in routing algorithms can take place without affecting any of the existing routers. By limiting the interplay between these two functions, we can develop them more easily.
Lesson 7 (T/F):
In the SDN approach, the SDN controller is physically located at each router that is present in a network.
False
TheSDN controlleris a logically centralized entity that acts as aninterface between the network elements and the network-control applications.
Lesson 7 (T/F):
By separating the control plane and the data plane, controlling the router’s behavior became easier using higher order programs. For example, it is easier to update the router’s state or control the path selection.
True
- Routing.The interdomain routing protocol used today, BGP, constrains routes. There are limited controls over inbound and outbound traffic. There is a set procedure that needs to be followed for route selection. Additionally, it is hard to make routing decisions using multiple criteria. With SDN, it is easier to update the router’s state, and SDN can provide more control over path selection.
Lesson 7 (T/F):
In the SDN approach, ISPs or other third parties can take up the responsibility for computing and distributing the router’s forwarding tables.
True
Lesson 7 (T/F):
Having the software implementations for SDNs controllers increasingly open and publicly available makes it hard to control, since any person could modify the software easily.
False
Lesson 7 (T/F):
In SDN networks, the SDN controller is responsible for the forwarding of traffic.
False
Lesson 7 (T/F):
The network-control applications are programs that manage the underlying network with the help of the SDN controller.
True
- SDN-controlled network elements
The SDN-controlled network elements, sometimes called the infrastructure layer, is responsible for the forwarding of traffic in a network based on the rules computed by the SDN control plane.**
- SDN controller
TheSDN controlleris a logically centralized entity that acts as aninterface between the network elements and the network-control applications.
- Network-control applications
The network-control applications are programs that manage the underlying network by collecting information about the network elements with the help of SDN controller.
Lesson 7 (T/F):
In SDN networks forwarding rules of traffic still have to be based on IP destination and cannot be based on other metrics, packet header info etc.
False
Lesson 7 (T/F):
SDN-controlled switches operate on the:
Data plane
or
Control plane
Data plane
What are the four defining features in an SDN architecture?
1)Flow-based forwarding:
- The rules for forwarding packets in the SDN-controlled switches can be computed based on any number of header field values in various layers such as the transport-layer, network-layer and link-layer.
2)Separation of data plane and control plane:
- The SDN-controlled switches operate on the data plane and they only execute the rules in the flow tables. Those rules are computed, installed, and managed by software that runs on separate servers.
Lesson 7 (T/F):
In an SDN Architecture, the northbound interface keeps track of information about the state of the hosts, links, switches and other controlled elements in the network, as well as copies of the flow tables of the switches.
False
- This layer is also known as the controller’s “northbound” interface using which the SDN controller interacts with network-control applications.
- Network-control applications can read/write network state and flow tables in controller’s state-management layer. The SDN controller can notify applications of changes in the network state, based on the event notifications sent by the SDN-controlled devices. The applications can then take appropriate actions based on the event.
- A REST interface is an example of a northbound API.
The question is actually asking about the Network-wide state-management layer:
- This layer is about the network-state that is maintained by the controller.
- The network-state includes any information about the state of the hosts, links, switches and other controlled elements in the network. It also includes copies of the flow tables of the switches.
- Network-state information is needed by the SDN control plane to configure the flow tables.
Lesson 7 (T/F):
In SDN networks, the southbound interface is responsible for the communication between SDN controller and the controlled devices.
True
Communication Layer
- The communication between SDN controller and the controlled devices is known as the “southbound” interface. OpenFlow is an example of this protocol, which is broadly used by SDN controllers today.
- This layer consists of a protocol through which the SDN controller and the network controlled elements communicate.
- Using this protocol, the devices send locally observed events to the SDN controller providing the controller with a current view of the network state. For example, these events can be a new device joining the network, heartbeat indicating the device is up, etc.
Lesson 7 (T/F):
In SDN networks, the controller needs to be implemented over a centralized server.
False
The SDN controller, although viewed as a monolithic service by external devices and applications, is implemented by distributed servers to achieve fault tolerance, high availability and efficiency. Despite the issues of synchronization across servers, many modern controllers such as OpenDayLight and ONOS have solved it and prefer distributed controllers to provide highly scalable services.
