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Exploring Network Programmability with Python and YANG


Recently, networking vendors and Silicon Valley giants have been putting forth a concerted effort to build standardized models for networking devices. These models allow for building reusable and versatile scripts with predictable, standardized data. Without such models, the wide variety of inputs and outputs required by different devices and vendors made scripting a tedious and challenging endeavor. The modeling language in use is called YANG, and a variety of standards have emerged. A vendor agnostic standard called OpenConfig has lately become stable enough to begin programming devices with it. Using Python, YANG is surprisingly easy to work with, and extremely powerful applications can be written with basic knowledge of JSON or XML and RPCs.

The talk will start with use-cases for programming networking devices, and will detail a specific, trivial, use case that will be used in the talk. Next, we will discuss the ‘legacy’ way of programming devices (SSH and screenscraping), and highlight the challenges, such as complex regular expressions, slow responses, and lack of reusability between devices. From there we will dive into YANG, focusing on OpenConfig models. A YANG model is essentially a template, and JSON or XML can be mapped to the YANG template. This makes it perfect for Pythonic manipulation. In the use case there will be a GET RPC returning a YANG representation of the box’s state in JSON, which we will search for the relevant health indicator by drilling down in the JSON dictionary. A simple change to the dictionary will remediate the problem, and a PATCH RPC merges the new configuration onto the box. Since open, standard models are in use, this script could be run on many devices across a network to achieve the same effect with no changes needed. We will finish up with the pros and cons of YANG before opening the talk for Q&A.


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