SDN is a service. openflow is a technology.

Many people do not understand the difference between openflow and Sdn. It is not surprising that these two technologies are closely related, so many people have such doubts. However, they are not interchangeable. Openflow is a protocol that uses a process like an API (Application Programming Interface) to set up a network switch. SDN is a term used to describe the highly automated configuration of network services by providing programmable interfaces within the network infrastructure. SDN terminology has been abused by many marketing personnel who use it in many technologies.

In fact, SDN can be clearly defined. An SDN network has three architecture layers: physical network, SDN application, and SDN controller. Let's take a look.

Physical Network. The underlying layer includes physical devices that constitute the foundation of all IT infrastructure in the network. We use the "Switch" concept because openflow changes the way Ethernet switches work. In this article, you can also consider the vswitch section in the physical infrastructure.

SDN application. The most visible layer in SDN design is the application that provides services (such as exchange/network virtualization, firewall and traffic balancer. (Note: The openflow-Based Load balancer is called a traffic balancer. They are not traditional load balancers because they cannot read packet content.) These applications are similar or identical to those in scenarios where the software runs on specialized hardware. Most of the coming innovations in network technology will take place in SDN applications.

SDN controller. SDN controllers are middleware and servers serve as the pivot of the entire architecture. The controller must be integrated with all physical and virtual devices in the network. The Controller abstracts physical network devices from SDN software that works with these devices. High Integration between controllers and network devices. In the openflow environment, the controller uses the openflow protocol and netconf protocol to communicate with the switch. (Openflow is the API for sending streaming data to the vswitch, while netconf is the API for network settings .)

SDN: Basic Architecture

In the current SDN mode, the vendor provides applications and a controller in a single product. For example, nicira/vmware encapsulates its applications and controllers in a single proprietary application stack. Cisco will embed the controller into the IOS software on the device to encapsulate its controller into the onepk product. Big Switch Networks recently released a commercial version of SDN controller, which provides two applications running on the Controller: Big virtual switch and big
Tap.

Obviously, the controller is a key part of the network architecture. It must present APIs to applications that represent useful functions. API is also the most competitive place for vendors to take the lead in the SDN market.

SDN
API: new battlefield

Cisco's onepk is also a southbound API. There is a lot of debate on whether openflow is sufficient to meet all network needs, especially regarding the migration from a packet-based network to a stream-based network. There are still some problems that may impede such migration, such as interoperability with existing protocols (such as STP and OSPF.