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Chapter 2. Understanding basic concepts in OpenDaylight

2.1. How does network virtualization work?

In the physical world, servers are connected by physical Ethernet switches and cables. Each server has a unique IP address and can either communicate directly or through IP routers. To access resources outside of the server domain, communication goes through external gateways to external servers that are protected from any unwanted communication by firewalls. In most cases, servers in different domains cannot talk to each other directly, unless such communication is specifically established.

Figure 2.1. Physical networks

Physical networks

When using server virtualization, it is necessary to provide a similar networking strategy for virtual machines (VMs). In a virtualized environment, multiple independent VMs from different domains can run on the same physical server simultaneously, and VMs from the same domain can run on different physical servers. The virtual compute loads require connectivity and security support similar to physical devices. Security is even more important when compute loads from different domains are hosted on the same server. Virtual devices from different domains can even use the same, overlapping, private IP addresses.

Figure 2.2. Compute and Network virtualization

Compute and Network virtualization

Networking support for virtual compute resources is called network virtualization, and it is addressed by software-defined networking (SDN) controllers. These environments can function independently from each other using tenant isolation.

2.2. What is software-defined networking?

Software-Defined Networking (SDN) is an approach for dynamically programming networks, including the ability to initialize, change, and manage network behaviour using open interfaces.

SDN often implies the physical separation of the network control plane from the forwarding plane such that a control plane can control several devices. The component that implements the SDN control plane is called an SDN controller.

Figure 2.3. Functions of the SDN controller

Functions of the SDN controller

To make SDN work, correctly define the interfaces between higher level management, orchestration systems, and the SDN controller (northbound APIs), as well as between the SDN controller and data plane elements (southbound APIs).

YOu can apply SDN to many use cases. OpenStack provides the foundation required to build a private or public cloud in which virtualized compute resources, and required networking and storage capabilities, can be dynamically instantiated and destroyed as required. This dynamic environment requires a programmable networking solution that is equally dynamic.

2.3. What is network functions virtualization?

In addition to basic networking, OpenDaylight can also be used with OpenStack to support network functions virtualization (NFV).

Network Functions Virtualization (NFV) is a software-based solution that helps the Communication Service Providers (CSPs) move beyond the traditional, proprietary hardware.

NFV virtualizes network functions such as firewalls and load balancers, so they can run on general purpose servers in a cloud-based infrastructure to provide more agility, flexibility, and scalability than legacy infrastructure.

SDN and NFV perform complementary functions in a virtualized network. NFV supports the virtualization of complex network functions, and SDN performs basic networking and forwards traffic to and between network functions.

For more information on NFV concepts, see the Network Functions Virtualization Product Guide.