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Evolving Technologies – Northbound vs. Southbound Protocols

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This is another post from my ongoing series here at AJSNetworking regarding Evolving Technologies. This addresses the Evolving Technologies section of the CCIE Written Exams. The complete list of topics and my previous posts can be found here:

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I think the best way to get a handle on the location of the Northbound and Southbound protocols  is to actually see them in relation to the other components. Remember, when we say network programmability, you should think Software Defined Networking (SDN). Figure 1 below makes this clear:

 Figure 1Evolving

Notice the “Northbound” APIs (protocols) communicate between your network management station running its network apps and the SDN controller. The “Southbound” APIs occur between the controller and the actual network devices themselves.

Northbound APIs

For the Northbound APIs, Cisco likes to use REST-based APIs. What is a REST-based API? A REST API, or an API that is RESTful (adheres to the constraints of REST) follows six constraints:

  • Client-Server – exists to maximize the portability of server-side functions to other platforms. This means that completely different applications, even in different languages, can use the same functions in a REST API.
  • Stateless – all state is kept client-side. The server does not retain any record of client state; results in a much more efficient SDN controller
  • Caching – just like cookies in your web browser. It is a good idea for the client to maintain a local copy of information that is commonly used; this improves performance and scalability.
  • Layered System – a REST API must be built in a way that a client interacts with it’s neighbor and does not need to see “beyond” that neighbor.
  • Uniform Interface – no matter the information retrieved, the method by which it is presented is always consistent.
  • Code-on-Demand – to transmit working code inside an API call.

A REST API is often just a Web server that accepts HTTP POSTs, GETs. These requests typically contain standard elements like XML, JSON, SOAP, or others.

Southbound APIs

What is common for the Southbound APIs? Cisco loves to keep it simple with the Command Line Interface (CLI) and Simple Network Management Protocol (SNMP).

Certainly the most well-known Southbound API is OpenFlow, but obviously there are other options available and in development. The Network Configuration Protocol (NetConf) uses Extensible Markup Language (XML) to communicate with the switches and routers to install and make configuration changes. Lisp, also promoted by ONF, is available to support flow mapping. In addition, there are more established networking protocols finding ways to run in an SDN environment, such as OSPF, MPLS, BGP, and IS-IS.

CCIE Emerging Technologies – SDN APIs

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CCIE Emerging Technologies

What is the glue that allows the Software Defined Networking (SDN) architecture to function so well? That communication process between the Control and Data planes? It is the Application Programming Interface or API.

What is a classic example of an API in the SDN world? The answer is OpenFlow.  Recall from other discussions here at AJSNETWORKING that the OpenFlow specification defines both a protocol between the control and data planes and an API by which the control plane can invoke the OpenFlow protocol.

 APIs are implemented by writing function calls in the program. This provides the linkage to the required subroutine for execution. An open or standardized API can ensure the portability of the application code and the vendor independence of the called service.

SDN controllers can be implemented directly on a server or on a virtual server. OpenFlow or some other open API is used to control the switches in the data plane. In addition, controllers use information about capacity and demand obtained from the networking equipment through which the traffic flows.

SDN controllers also expose northbound APIs. As we have discussed here at the blog, this allows developers and their network engineers to deploy a wide range of off-the-shelf and custom-built network applications. Obviously, many of these applications were never before possible before SDN.

As yet there is no standardized northbound API nor a consensus on an open northbound API. A number of vendors offer a REpresentational State Transfer (REST)-based API to provide a programmable interface to their SDN controller.

Also envisioned but not yet defined are horizontal APIs (east/westbound), which would enable communication and cooperation among groups or federations of controllers to synchronize state for high availability.

At the application plane are a variety of applications that interact with SDN controllers. SDN applications are programs that may use an abstract view of the network for their decision-making goals. These applications convey their network requirements and desired network behavior to the SDN controller via a northbound API. Examples of applications are energy-efficient networking, security monitoring, access control, and network management.

Want more information – check out the excellent – Foundations of Modern Networking: SDN, NFV, QoE, IoT, and Cloud