Category Archives: CCIE SP

Evolving Technologies – Scripting

CCIE Coaching, CCIE Data Center, CCIE General, CCIE R&S, CCIE Security, CCIE SP, ,

scripting

Network management tools often create more frustration for network engineers than problem they can solve. This is true for a number of reasons, including:

  • Many of them are difficult to install and maintain
  • They are often proprietary and support only a single vendor
  • They often lack scalability and reliability

As a result, many engineers give up and instead rely on the command-line interface (CLI) to manage individual switches. An increasing number of network engineers stretch the limitations of those tools by writing scripts in TCL, Perl, Python or other languages.

Of course these engineers are not writing sophisticated software, just scripts that allow them to scale certain tasks, such as reconfiguring multiple switches using a screen scraping of CLI commands.

Scripting is a critical component of many Software Defined Networking (SND) implementations – including that of Cisco Systems with the Application Centric Infrastructure (ACI).

We know that in this technology, Cisco likes to use REST as the Northbound API. Yet Cisco engineers prefer to use Python instead of sending plain vanilla REST calls. This is because Python allows the parsing of command line options and configurations. Of course it is possible to use Python with sample scripts to turn XML into REST calls, but this approach requires formatting the XML configuration files according to the ACI object model. This results in scripts that are shared requiring administrators to have knowledge of this ACI object model.

The Python SDK for ACI permits the creation of scripts with configuration files and command line options that anyone skilled in networking can use. The ACI SDK provides models that enable you to perform all the operations that the Cisco ACI fabric offers with several advantages:

  • Python can parse configuration files in whichever format you prefer
  • The SDK APIs can be identical over time, while the specific format of the XML object model can change
  • You can perform more sophisticated conditional operations, string manipulations, etc

Evolving Technologies – Northbound vs. Southbound Protocols

CCIE Coaching, CCIE Data Center, CCIE General, CCIE R&S, CCIE Security, CCIE SP, , ,

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:

Free Evolving Technologies Training!

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.