OpenDaylight, hosted by the Linux Foundation, provides an open, modular and flexible SDN platform. It is composed of a number of different projects that can be combined together into a solution that meets the requirements of a given scenario, and can, therefore, cover many different use-cases.

To learn more, visit this OpenDaylight website, where you can find further information on various uses of OpenDaylight.

Red Hat’s OpenDaylight focuses on network control and virtualization. OpenDaylight is co-engineered with the Red Hat OpenStack Platform and used as a backend service for OpenStack Networking (neutron) to provide the networking infrastructure for your Red Hat OpenStack cloud.

In the physical world, servers are mutually connected by physical Ethernet switches and cables. Each of them has a unique IP address and can either communicate directly or through IP routers. To access resources outside 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

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 may run on the same physical server simultaneously, and VMs from the same domain may run on different physical servers. The virtual compute loads still require similar connectivity and security support as they would have in physical devices. Security becomes even more important when compute loads from different domains are hosted on the same server. Furthermore, virtual devices from different domains may even use the same, overlapping, private IP addresses.

Figure 2.2. Compute and Network virtualization

Networking support for virtual compute resources is referred to as network virtualization, and is a common problem solved by Software-defined Networking (SDN) controllers. These environments can function independently from each other using tenant isolation.

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

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

Figure 2.3. Functions of the SDN controller

To make SDN work, there must be well-defined interfaces both between higher level management and orchestration systems and the SDN controller (northbound APIs) as well as between the SDN controller and data plane elements (southbound APIs).

SDN has broad applicability to many use cases. One area in which SDN has proved essential is cloud computing in general, and OpenStack in particular. OpenStack provides the foundation to build a private or public cloud in which virtualized compute resources, together with required networking and storage, can be dynamically instantiated and destroyed as needed. This dynamic environment requires a programmable networking solution that is equally dynamic — in other words, OpenStack needs SDN.

Later, you will learn more about how OpenDaylight is used as an SDN controller for OpenStack.

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 to achieve greater efficiency and agility while reducing operational costs.

NFV virtualizes network functions (for example, firewalls and load balancers) so they can run on a general-purpose servers in a cloud-based infrastructure to provide more agility, flexibility, simplicity, efficiency, and scalability than legacy infrastructure, while also reducing costs and allowing greater innovation.

SDN and NFV perform complementary functions in a virtualized network. NFV supports the virtualization of complex network functions while SDN is used to perform basic networking, and forward traffic to and between network functions.

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

The platform also provides a framework for Authentication, Authorization and Accounting (AAA), and enables automatic identification and hardening of network devices and controllers.

The northbound API, which is used to communicate with the OpenStack Networking service (neutron), is primarily based on REST. The Model-Driven Service Abstraction Layer (described later) renders the REST APIs according to the RESTCONF specification based on the YANG models defined by the applications communicating over the northbound protocol.

The business logic of the controller is defined in Services and Applications. The basic overview of services and applications available with the Boron release can be found on the OpenDaylight Boron release web page. A more detailed view can be obtained from the Project list. The OpenDaylight project offers a variety of applications, but usually only a limited number of the applications is used in a production deployment.

The Model-Driven Service Abstraction Layer (MD-SAL) is the central component of the Red Hat OpenDaylight platform. It is an infrastructure component that provides messaging and data storage functionality for other OpenDaylight components based on user-defined data and interface models.

MD-SAL, in MD-SAL based applications, uses the YANG models to define all required APIs, including inter-component APIs, plug-in APIs and northbound APIs. These YANG models are used by the OpenDaylight YANG Tools to instantly generate Java-based APIs. These are then rendered according to the RESTCONF specification into the REST APIs and provided to applications communication over the northbound protocol.

Using YANG and YANG Tools to define and render the APIs greatly simplifies the development of new applications. The code for the APIs is generated automatically which ensures that provided interfaces are always consistent. As a result, the models are easily extendable.

Applications typically use the services of southbound plug-ins to communicate with other devices, virtual or physical. The basic overview of southbound plug-ins available with the Boron release can be found on the OpenDaylight Boron release web page. The Project list shows them in more details.

The Red Hat OpenDaylight solution (part of the Red Hat OpenStack Platform) consists of the five main parts, but the selection of applications and plug-ins is limited to a certain number only. The Controller platform is based on the NetVirt application. This is the only application currently supported by Red Hat. In the future releases, more applications will be added.

Most applications will only use a small subset of the available southbound plug-ins to control the data plane. The NetVirt application of the Red Hat OpenDaylight solution uses OpenFlow and Open vSwitch Database Management Protocol (OVSDB).

The overview of the Red Hat OpenDaylight architecture is shown in the following diagram.

Figure 3.2. Red Hat OpenDaylight architecture

The Red Hat OpenStack Platform director is a toolset for installing and managing a complete OpenStack environment. Starting with Red Hat OpenStack Platform 10, director can deploy and configure OpenStack to work with OpenDaylight. OpenDaylight can run together with the OpenStack overcloud controller role, or as a separate custom role on a different node.

For more information, see the OpenDaylight and Red Hat OpenStack Installation and Configuration Guide.

OpenDaylight provides the required Layer 2 (L2) connectivity among VM instances belonging to the same neutron virtual network. Each time a neutron network is created by a user, OpenDaylight automatically sets the required Open vSwitch (OVS) parameters on the relevant compute nodes to ensure that instances, belonging to the same network, can communicate with each other over a shared broadcast domain.

While VXLAN is the recommended encapsulation format for tenant networks traffic, 802.1q VLANs are also supported. In the case of VXLAN, OpenDaylight creates and manage the virtual tunnel endpoints (VTEPs) between the OVS nodes automatically to ensure efficient communication between the nodes, and without relying on any special features on the underlying fabric (the only requirement from the underlying network is support for unicast IP routing between the nodes).

VM instances get automatically assigned with an IPv4 address using the DHCP protocol, according to the tenant subnet configuration. This is currently done by leveraging the neutron DHCP agent. Each tenant is completely isolated from other tenants, so that IP addresses can overlap.

OpenDaylight provides support for Layer 3 (L3) routing between OpenStack networks, whenever a virtual router device is defined by the user. Routing is supported between different networks of the same project (tenant), which is also commonly referred to as East-West routing.

OpenDaylight uses a distributed virtual routing paradigm, so that the forwarding jobs are done locally on each compute node.

A floating IP is a 1-to-1 IPv4 address mapping between a floating address and the fixed IP address, assigned to the instance in the tenant network. Once a VM instance is assigned with a floating IP by the user, the IP is used for any incoming or outgoing external communication. The Red Hat OpenStack Platform director includes a default template, where each compute role has external connectivity for floating IPs communication. These external connections support both flat (untagged) and VLAN based networks.

OpenDaylight provides support for tenant configurable Security Groups that allow a tenant to control what traffic can flow in and out VM instances. Security Groups can be assigned per VM port or per neutron network, and filter traffic based on TCP/IP characteristics such as IP address, IP protocol numbers, TCP/UDP port numbers and ICMP codes.

By default, each instance is assigned a default Security Group, where egress traffic is allowed, but all ingress traffic to the VM is blocked. The only exception is the trusted control-plane traffic such as ARP and DHCP. In addition, anti-spoofing rules are present, so a VM cannot send or receive packets with MAC or IP addresses that are unknown to neutron. OpenDaylight also provides support for the neutron port-security extension, that allows tenants to turn on or off security filtering on a per port basis.

OpenDaylight implements the Security Groups rules within OVS in a stateful manner, by leveraging OpenFlow and conntrack.