Archive

Category Archives for "TTL255 – Przemek Rogala’s blog"

Developing NetBox Plugin – Part 5 – Permissions and API

In previous installments of this series we built out a fully functional plugin dedicated to tracking Bgp Peering connections. In this post we'll add final components: object permissions and API views.

Developing NetBox Plugin tutorial series

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Adding permissions

Right now all users can view, edit and delete Bgp Peering objects. In the production system we would like to be able to have more granular control over who can perform a given operation. This is where the permissions system comes in.

In our plugin we will leverage Django authentication system [1] to enable permissions for views we built out.

Adding permissions to views

Below are the changes I made to views.py to Continue reading

Developing NetBox Plugin – Part 4 – Small improvements

Welcome to part 4 of the tutorial on developing NetBox plugin. By now BgpPeering plugin is functional but there are few things here and there that could make it better. In this post, we'll go through many improvements that will make the plugin look better and increase its functionality.

Developing NetBox Plugin tutorial series

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Updating display name of BgpPeering objects

We'll start improvements by changing default display name of BgpPeering Continue reading

Developing NetBox Plugin – Part 3 – Adding search panel

Welcome to part 3 of my tutorial walking you through process of developing NetBox plugin. In part 2 we added basic web UI views to our BgpPeering plugin. In this post we'll add search panel to list view to allow us to search/filter Bgp Peering objects.

Developing NetBox Plugin tutorial series

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Introduction

List view we created for displaying all Bgp Peering objects in one place is very useful. However it will become difficult to find items of interest once we have more than 30-50 objects. For that purpose we should add means of filtering objects to the ones that meet certain criteria.

Other objects in NetBox already have filtering functionality and use search panel located to the right of object tables. Continue reading

Developing NetBox Plugin – Part 2 – Adding web UI pages

Welcome to part 2 of my tutorial walking you through process of developing NetBox plugin. In part 1 we set up our development environment and built base version of Bgp Peering plugin. Here we will continue work on the plugin by adding UI pages allowing us to list, view and add, Bgp Peering objects.

Developing NetBox Plugin tutorial series

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Disclaimer

Original version of this post contained views that Continue reading

TTL255 finalist of Cisco 2020 IT Blog Awards

I'm excited to announce that TTL255.com is one of the finalists in the Most Educational category of the 2020 IT Blog Awards, hosted by Cisco.

Over the years I learned great deal from blogs and videos created by community members. At one point I realized that I also might have something to offer and started this blog to give back to community hoping to teach and inspire others.

Creating valuable technical content takes a lot of work and time commitment. After years of posting here I appreciate even more all content makers out there that often don't ask for anything in return.

This year I decided to submit TTL255.com to 2020 IT Blog Awards hoping to reach more people and see where that takes me.

If you find my content valuable and worth your time, please consider voting for TTL255.com by following the below link:

https://www.ciscofeedback.vovici.com/se/705E3ECD2A8D7180

ITBlogAwards_2020_Badge-Finalist-MostEducational

You can find me in the Most Educational category:

blog-awards-entry

While you there have a look at other amazing blog posts. Some of them might inspire you, some will teach you something new. All come from members of community that put themselves out there to share their knowledge with Continue reading

Developing NetBox Plugin – Part 1 – Setup and initial build

This is first post in my series showing how to develop NetBox plugin. We'll talk about what NetBox plugins are and why would you want one. Then I'll show you how to set up development environment. We'll finish by building base version of our custom plugin.

Developing NetBox Plugin tutorial series

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What are NetBox plugins?

NetBox plugins are small, self-contained, applications that add new functionality. This could range from adding new API endpoint to fully fledged apps. These apps can provide their own data models, views, background tasks and more. We can also inject content Continue reading

Ansible – ‘until’ loop

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Introduction

In this short post I'll introduce you to lesser known type of Ansible loop: "until" loop. This loop is used for retrying task until certain condition is met.

To use this loop in task you essentially need to add 3 arguments to your task arguments:

until - condition that must be met for loop to stop. That is Ansible will continue executing the task until expression used here evaluates to true.
retry - specifies how many times we want to run the task before Ansible gives up.
delay - delay, in seconds, between retries.

As an example, below task will keep sending GET request to specified URL until the "status" key in response is equal to "READY". We ask Ansible to make 10 attempts in total with delay of 1 second between each attempt. If after final attempt condition in until is still not met task is marked as failed.

  - name: Wait until web  Continue reading

Jinja2 Tutorial – Part 6 – Include and Import

Welcome to another instalment in my Jinja2 Tutorial series. So far we've learned a lot about rendering, control structures and various functions. Here we'll start discussing language features that help us deal with organizing templates. First constructs we'll look at are include and import statements.

Jinja2 Tutorial series

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Introduction

Include and Import statements are some of the tools that Jinja gives us to help with organizing collections of templates, especially once these grow in size.

By using these constructs we can split templates into smaller logical units, leading to files with well-defined scopes. This in turn will make it easier to Continue reading

Jinja2 Tutorial – Part 5 – Macros

Welcome to the part 5 of Jinja2 Tutorial where we learn all about macros. We'll talk about what macros are, why we would use them and we'll see some examples to help us appreciate this feature better.

Jinja2 Tutorial series

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What are macros?

Macros are similar to functions in many programming languages. We use them to encapsulate logic used to perform repeatable actions. Macros can take arguments or be used without them.

Inside of macros we can use any of the Jinja features and constructs. Result of running macro is some text. You can essentially treat macro as Continue reading

Use Python to translate TCP/UDP port numbers to names

This short post shows how you can use Python to convert TCP/UDP port number to port name and vice versa.

Most of us know names of common TCP and UDP ports like 22/ssh, 23/telnet, 80/http or 443/https. We learn these early in our networking careers and many of them are so common that even when woken up middle of the night you'd know 53 is domain aka dns!

But there are also many not-so commonly used ports that have been given names. These ones sometimes show up in firewall logs or are mentioned in literature. Some vendors also try to replace numeric value with a human readable name in the configs and outputs of different commands.

One way or the other, I'd be good to have an easy method of getting port number given its name, and on occasion we might want to get name of particular port number.

There are many ways one could achieve that. We might search web, drop into documentation, or even check /etc/services if we have access to Linux box.

I decided to check if we can do some programmatic translation with Python, seeing as sometimes we could have hundreds of entries to process and Continue reading

Build DSCP to ToS conversion table with Python

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Introduction

In this post we're going to write Python program that generates DSCP to ToS conversion table while avoiding hardcoding values as much as possible. We will then save the final table to csv file with pre-defined column headers.

I got the idea for this blog article from the tweet posted the other day by Nick Russo. I thought it is an interesting problem to tackle as similar ones pop up all the time during early stages of Network Automation journey. What makes this challenge great is that it requires us to carry out tasks that apply to writing larger programs.

  • We need to understand the problem and possibly do some research.
  • We have to come up with plan of action.
  • We need to break down larger tasks into smaller pieces.
  • We need to implement all Continue reading

Vrnetlab – Run virtual routers in Docker containers

It’s time to have a look at some Network Automation tools. Today I want to introduce you to Vrnetlab, great piece of software that allows you to run virtual routers inside Docker containers. We’ll talk about what Vrnetlab does and what are its selling points. Then we’ll see how to bring up lab devices by hand and how to use them.

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Vrnetlab overview

Vrnetlab provides convenient way of building virtualized network environments by leveraging existing Docker ecosystem.

This means that you can take image of virtual appliance provided by the vendor and use Vrnetlab to create containers for it. The selling point here is that the whole tool-chain was created with automation in mind, that is you can build your network automation CI pipeline on top of Vrnetlab and no human is needed to spin up the environment, and run Continue reading

Jinja2 Tutorial – Part 4 – Template filters

This is part 4 of Jinja2 tutorial where we continue looking at the language features, specifically we'll be discussing template filters. We'll see what filters are and how we can use them in our templates. I'll also show you how you can write your own custom filters.

Jinja2 Tutorial series

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Overview of Jinja2 filters

Let's jump straight in. Jinja2 filter is something we use to transform data held in variables. We apply filters by placing pipe symbol | Continue reading

YAML anchors and aliases and how to disable them

Introduction

In this short post I explain what are YAML aliases and anchors. I then show you how to stop PyYAML from using these when serializing data structures.

While references are absolutely fine to use in YAML files meant for programmatic consumption I find that it sometimes confuses humans, especially if they’ve never seen these before. For this reason I tend to disable anchors and aliases when saving data to YAML files meant for human consumption.

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YAML aliases and anchors

YAML specification has provision for preserving information about nodes pointing to the same data. This basically means that if you have some data that is referenced in multiple places in your data structure then YAML dumper will:

  • add an anchor to the first occurrence
  • replace any subsequent occurrences of that data with aliases

Now, how do these anchors and aliases look like?

&id001 - example of an anchor, placed with the first occurrence of data
*id001 - example of an alias, replaces subsequent occurrence Continue reading

Jinja2 Tutorial – Part 3 – Whitespace control

Text documents are the final result of rendering templates. Depending on the end consumer of these documents whitespace placement could be significant. One of the major niggles in Jinja2, in my opinion, is the way control statements and other elements affect whitespace output in the end documents.

To put it bluntly, mastering whitespaces in Jinja2 is the only way of making sure your templates generate text exactly the way you intended.

Now we know the importance of the problem, time to understand where it originates, to do that we’ll have a look at a lot of examples. Then we'll learn how we can control rendering whitespaces in Jinja2 templates.

Jinja2 Tutorial series

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