Automating Junos Administration

Foreword

As someone reading a book on network automation, you’re clearly aware of the benefits of automation, the cost of human mistakes, and the ability of software to perform routine tasks with accuracy, diligence, caution, and reliability. Automation can add robustness and fluidity to your network, prevent outages, and decrease the impact of networking issues and the mean time to resolution.

In my work as the architect and coder of the JUNOS user interface, I’ve preached automation since the early days. We knew automation would be a key differentiator for our customers and wanted to allow application programmers to escape the world of “screen scraping,” where command-line interface (CLI) output designed for readability and human digestion is filtered using regular expressions to extract useful information, a process that is error prone, fragile, and difficult to maintain. If a change is made to the CLI to add a new data item to the output or the format of the output is changed, a regular expression may fail to match correctly, leading to errors that cannot be easily detected.

We built into JUNOS an XML-based API that would allow immediate access to data items in a robust, simple, and future-proof way. XPath expressions can extract specific data values while ignoring new content or changes in the way values are organized. Complex expressions can find precise values such as the remote address of every point-to-point link that has a large MTU and high error rates.

We also knew that ...