1. Overview

What You’ll Learn

• Introduction to Cisco DNA Center SDK
• Understand Command Runner and usage
• Code a configuration manager

What You’ll Need

• Set up Python 3.x
• Use your IDE of choice
• Install Cisco DNA Center SDK
• Access a Cisco DNA Center instance

2. Hello! DNA Center SDK

Install DNA Center SDK

Just like any API or tool, your first stop is to check out the documentation:

• Cisco DNA Center SDK Doc

• Installing SDK is simple. In your terminal, execute:

pip install dnacentersdk

Quick Start: Let’s Authenticate Using the SDK

By default, DNA Center SDK will look for the following environment variables to create new connection objects:

• DNA_CENTER_USERNAME: HTTP Basic Auth username
• DNA_CENTER_PASSWORD: HTTP Basic Auth password
• DNA_CENTER_BASE_URL: The base URL to be prefixed to the individual API endpoint suffixes

In our case, we will not use environment variables. We will add it to part of our Python code.

Let’s Get Started!

1: Clone the code repo.

In your terminal, run:

git clone https://github.com/CiscoLearning/dnac-config-manager.git

Kick-start Python in interactive mode:

python3

• You can copy and paste the Python code snippets while in Python interactive mode.*

2: Import the DNA Center SDK.

from dnacentersdk import DNACenterAPI

3: Define the connection string.

In this case, we will create a Python dictionary with the connection string:

dnac_creds = {}
dnac_creds['url'] = 'https://sandboxdnac.cisco.com'
dnac_creds['username'] = 'devnetuser'
dnac_creds['password'] = 'Cisco123!'

4: Instantiate “Connection Object.”

dnac = DNACenterAPI(username=dnac_creds['username'], password=dnac_creds['password'], base_url=dnac_creds['url'], verify=False)

5: Display your Auth Token.

print("Auth Token: ", dnac.access_token)

6: Let’s look at the completed script.

Head over to the working directory from our cloned repo and run the Authentication.py file:

cd dnac-config-manager/
ls -al

7: Run it.

python Authentication.py

3. What Is Command Runner?

Now that we have an understanding on how the DNA Center SDK works and we’ve authenticated, let’s build our use case!

Use Case Definition

I’d like to be able to take a snapshot of all of the device config to detect configuration drift and have a golden image.

Use Case Workflow

• Authenticate
• Get a list of all managed network devices
• Use Command Runner to retrieve the running config
• Save to a file

What Is Command Runner?

Command Runner is a feature in Cisco DNA Center that allows you to execute a handful of read-only (for now) Cisco IOS commands on the devices managed by DNA Center.

Here is how you can get a list of all supported Cisco IOS commands:

commands = dnac.command_runner.get_all_keywords_of_clis_accepted()

⚠️ Cisco DNA Center API calls are asynchronous, which means that for each executed task, a task ID is created. Upon task completion, content can be retrieved from the /file endpoint.

API endpoints that we are planning on using:

• POST /dna/system/api/v1/auth/token
• GET /dna/intent/api/v1/network-device
• POST /dna/intent/api/v1/network-device-poller/cli/read-request
• GET /dna/intent/api/v1/task/{task_id}
• GET /dna/intent/api/v1/file/{file_Id}

SDK methods that we are planning on using:

• Authentication
• devices.get_device_list()
• command_runner.run_read_only_commands_on_devices()
• task.get_task_by_id()
• file.download_a_file_by_fileid()

Let’s Code It!

4. Code IT! Config. Manager

Code Use Case

Device Config Backup

0: Using your IDE of choice, create a new ‘.py’ file and import libraries.

Click the + sign next to the cloned folder ciscolive-devwks-2107:

from dnacentersdk import DNACenterAPI
import json
import warnings

1: Authenticate.

By now, we know how to do this. We need to pass Basic Auth and capture our API token.

Copy this step to the editor last; this needs to be at the end of the file.

if __name__ == '__main__':
    dnac_creds = {}
    dnac_creds['url'] = 'https://sandboxdnac.cisco.com'
    dnac_creds['username'] = 'devnetuser'
    dnac_creds['password'] = 'Cisco123!'

    dnac = DNACenterAPI(username=dnac_creds['username'], password=dnac_creds['password'], base_url=dnac_creds['url'],
                        verify=False)
    print("Auth Token: ", dnac.access_token)
    print("Gathering Device Info ... \n")
    get_device_list()

2: Retrieve a list of devices.

• Use the devices class to call the get_device_list() method to retrieve a list of all managed devices.
• Upon 200 OK, loop through the list of Switches and Hubs and extract the device ID. We need to leverage it to programmatically run the command on each device.
• Access the device ID variable via device.id and pass it to and call the cmd_run() function (we will build next).

Notice anything?

"""
This function handles getting device list
"""
def get_device_list():
    devices = dnac.devices.get_device_list()
    devicesuid_list = []
    for device in devices.response:
        if device.family == 'Switches and Hubs':
            print("Managed Device IP: {} ".format(device.managementIpAddress))
            devicesuid_list.append(device.id)
    print("\n")
    cmd_run(devicesuid_list)

3: Initiate Command Runner.

• As we iterate over each device, we will need to execute the show run command. To do so, use the command_runner class and call read run_read_only_commands_on_devices() method. This method requires two inputs of type list: commands and deviceUuids.
• Upon execution, DNA Center will return a taskId (asynchronous, remember?).
• Check its progress via the task class by calling the get_task_by_id() method. Once the task has been successfully executed (you can use the built-in error handling within the SDK to check, but that’s for another blog post), grab the returned fileId.
• Now, simply access the file class and call the download_a_file_by_fileid() method … and VOILA!

"""
This function handles command runner execution
"""
def cmd_run(device_list):
    for device in device_list:
        print("Executing Command on {}".format(device))
        run_cmd = dnac.command_runner.run_read_only_commands_on_devices(commands=["show run"], deviceUuids=[device])
        print("Task started! Task ID is {}".format(run_cmd.response.taskId))
        task_info = dnac.task.get_task_by_id(run_cmd.response.taskId)
        task_progress = task_info.response.progress
        print("Task Status : {}".format(task_progress))
        while task_progress == 'CLI Runner request creation':
            task_progress = dnac.task.get_task_by_id(run_cmd.response.taskId).response.progress
        task_progress= json.loads(task_progress)
        cmd_output = dnac.file.download_a_file_by_fileid(task_progress['fileId'], dirpath='file.json', save_file=True)
        print("Saving config for device ... \n")

Run It!

5. Congratulations

Congratulations! You’ve successfully completed this tutorial!

This is a great example of configuration management. You could use this as a base to start building out a simple configuration drift monitoring tool, given that the config is returned as JSON data. We can easily use a JSON query to check for any configuration drift and automatically rebase it to the original config.

This can be taken a step further even by leveraging Git for version control of your device config.

Learn More

• Cisco Learning Network DevNet Certifications Community
• DevNet Associate Certification
• ENAUTO Certification
• Cisco U. Tutorials