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Rowell Dionicio

Networking, security, and entrepreneurship

Archives for February 2020

I Passed the DevNet Associate Exam!

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Cisco DevNet launched in 2014 under Susie Wee. On February 24th, 2020 they released their brand new DevNet Associate certification, along with other DevNet certifications.

I remember seeing the DevNet Zone at Cisco Live about three years ago, and I was intrigued. Where was Cisco going with this?

Late in 2019, I decided to take a bigger step towards network automation and scripting with Python. I saw that it would be inevitable and it would surely enhance how I configure, manage, and troubleshoot networks.

That’s when I began dedicating time to learning Python and how it relates to DevNet. I’ve even started writing content about the DevNet Associate which will soon turn into videos.

DevNet Associate Certification

The DevNet Associate (DEVASC 200-901 version 1.0) was an excuse for me to learn Python. Since 2018, I’ve always told myself that I would learn Python to make scripts.

I didn’t follow through with that until 2019.

On February 26th, 2020, I took the DevNet Associate exam and passed! Surprisingly, I even made it into the DevNet 500, the first 500 people worldwide to obtain a DevNet certification!

Cisco DevNet Associate + DevNet 500

I’ll preface everything with, “I’m not a programmer.” But I do have the drive to learn. That’s what’s important here. Do you have a purpose other than just obtaining a certification?

How hard is the DevNet Associate?

With that said, I felt the DevNet Associate exam was very challenging for me. Why? Because the concepts are all very new to me. I’m learning so many different topics all at once, from Python to programming methodologies, to APIs and how APIs work with different Cisco technologies.

I felt the DevNet Associate was as challenging when I first took my Cisco CCNA so many years ago. It was a refreshing take, exciting, taking on a new topic.

Do you need programming and networking experience?

Without any programming experience, it will be challenging. If you already have programming experience with Python and APIs, it will give you an upper-hand.

You don’t need real-world programming experience to take this exam but it does help to have it. At the minimum you should practice with labs.

There is a small section of the DevNet Associate dedicated to networking concepts. If you don’t have any networking experience, then you’ll need to pick up some basics. Check the objectives for what you need to cover. If you’re a network administrator or network engineer, you can pass these questions with ease.

How did I study for the DevNet Associate?

I started actively studying for the DevNet Associate exam in October 2019. The certification was announced during Cisco Live 2019 in San Diego. There were no study guides available at the time so I relied 100% on labs.

Mid-2019 I started using Todoist to track my tasks and on August 10th, 2019 I added a daily task to Practice Python.

Creating a daily task in Todoist

I wasn’t able to practice it every single day but I was reminded to. It helps to install Python on your computer and learn from the labs over at developer.cisco.com (you’ll need to create a free account).

The DevNet page outlines a set of labs, although not a definitive list, you can take that map back to some of the objectives. I did every single one of those labs. Some of them I did repeatedly.

A resource that helped as well are the APIs from Meraki. I have access to Meraki environments which allowed me to test out my GET requests in a Python script.

Meraki actively maintains a Sandbox in which you can test against using the labs I mentioned earlier or you can use Postman to test API access.

The majority of my time was spent testing out API access, running other people’s scripts, and understanding how they ran.

Other parts of the objectives will require research into learning about CI/CD, methodologies, etc.

You will be tested fairly on this exam. I highly recommend learning how to write an API request and understand the different components relating to it. Don’t forget to learn how APIs are leveraged with other Cisco platforms such as routers, switches, SD-WAN, DNA Center, ACI, UCS, etc. This is a Cisco vendor exam so you should be able to describe these capabilities and their differences. 15% of the exam objectives is for Cisco Platforms and Development.

Cisco has plenty of resources around DevNet Associate from YouTube, DevNet Create, Cisco Live videos (sign up to watch these), and other contributors via blog or video.

Surround yourself with other DevNet Associate candidates on Twitter, WebEx Teams, other Cisco Champions, Slack channels, etc. It’s what I’ve done to help me get into the right mindset.

The Cisco DevNet certifications are much more than just getting a certification. For me, it’s encouragement and validation into what I’m learning. It’s the community surrounding this movement. It’s advancement in skills and in a career. It’s building efficiency and solutions to today’s problems. So today, I’m figuring out how to write a script to parse the Cisco IOS output. Wish me luck!

Are you studying for the DevNet Associate?

Let me know in the comments below.

Python – Parsing Cisco AireOS Configuration

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I’m beginning to get the hang of Python and it’s capabilities with network operations/monitoring.

My good friend and co-host on the CTS Podcast, François Vergès, has been creating his own scripts to help automate some of the operational tasks he does with Cisco AireOS WLAN controllers.

There was a scenario where I wanted to gather the operating channel and transmit power of a specific number of access points joined to a Cisco 8540 controller.

We can simply look at this via the management GUI or create some sort of Cisco Prime report but I just wanted a simple CLI output.

Cisco AireOS has a CLI command to get this output for the 2.4 GHz and 5 GHz radio:

show advanced 802.11a|b summary

The result of the command is every single access point on the controller but I just wanted a subset of those access points. That’s where I need to match a specific pattern based on the access point name using REGEX.

With this script, I am using Python 3.7 with the Regular expression operations library and netmiko library.

François was able to point me in the right direction with using the ConnectHandler to create a my connection and send the command to the WLAN controller:

import re
from netmiko import ConnectHandler

with ConnectHandler(
    ip = 'big-wlan-controller',
    port = 22,
    username = 'admin',
    password = 'test123',
    device_type = 'cisco_wlc_ssh'
) as ch:

    output = ch.send_command("show advanced 802.11a summary")

The full output of the command is placed into a variable called output.

Now, I wanted to use REGEX to match on specific access points. I create a pattern and use a for loop on each line in the variable of output.

pattern = re.compile("b2", re.IGNORECASE)
for ap in output.splitlines():
    if pattern.search(ap) != None:
        print(ap)

In the pattern variable I am using REGEX to simply search for anything containing “b2” which stands for Building 2 in my scenario.

In the for loop, I am taking the output variable and splitting the string by line and applying the pattern search per line. Then I print the output to the screen.

The full script:

import re
from netmiko import ConnectHandler

with ConnectHandler(
    ip = 'big-wlan-controller',
    port = 22,
    username = 'admin',
    password = 'test123',
    device_type = 'cisco_wlc_ssh'
) as ch:

    output = ch.send_command("show advanced 802.11a summary")

pattern = re.compile("b2", re.IGNORECASE)
for ap in output.splitlines():
    if pattern.search(ap) != None:
        print(ap)

The output (sanitized):

$ python regex-test.py
b2-ap-1                     xx:xx:xx:xx:xx:xx  1   ENABLED  UP          (108,112)           3/6 (11 dBm)
b2-ap-2                     xx:xx:xx:xx:xx:xx  1   ENABLED  UP          (100,104,108,112)  *1/7 (19 dBm)
b2-ap-3                     xx:xx:xx:xx:xx:xx  1   ENABLED  UP          52*                *1/6 (17 dBm)
b2-ap-4                     xx:xx:xx:xx:xx:xx  1   ENABLED  UP          36*                *2/5 (12 dBm)
b2-ap-5                     xx:xx:xx:xx:xx:xx  1   ENABLED  UP          136*               *1/6 (17 dBm)

From the output I can see the AP name, MAC address of the AP, up/down status, operating channel, and transmit power. There’s a bit more work to put into the script but it gave me exactly what I needed at the time.