7 Python Scripts for Network Engineers

In this post I will cover in detail 7 Python scripts that I use as a Network Engineer to make my life easier.

Check out more Python for Network Engineers posts.

For each example that needs connectivity I will be using a basic topology of 20 x CSR routers.

I will also be using Netmiko to connect to the network devices. If you have not used Netmiko before you can check this quick run through of creating a connection to a Cisco router using Netmiko

1. SSH to router using Python

So the first script I am going to show you is how to SSH to an IOS device. This is the main reason for using Python for Network Automation. Connect to a network device and then do stuff!

This script uses Netmiko to make the connection and then I will run ‘show ip interface brief’ command to verify the ip interfaces on the router.

#!/usr/bin/python

from netmiko import ConnectHandler

CSR = {
    'device_type': 'cisco_ios',
    'ip': '192.168.1.220',
    'username': 'roger',
    'password': 'cisco'
}

net_connect = ConnectHandler(**CSR)
output = net_connect.send_command('show ip int brief')
print (output)

connection.disconnect()

This is a very basic script, which first imports from Netmiko the ConnectHandler.

Note: To run this you must have first installed Netmiko – if you have not please watch the video at the top of this post.

We then define a device called CSR and provide the information that Netmiko requires, which are device_type, IP address and a username and password.

Then using the net_connect module you connect to the device CSR

Once connected we send the command ‘sh ip int brief’ to the router and save the value as output

Finally we print output and disconnect from the device.

2. SSH to multiple routers

Now we have a basic connection to a single router, it’s time to scale it out, we are now going to connect to 5 routers. But it could easily be 100 or 1000!

For this I have created a new file called devices.txt which contains all the IP addresses of our 5 x CSR routers. We then use the same script but loop through the connection and pass in the IP of each router so we can get the ‘sh ip int brief’ output of all the routers.

192.168.1.220
192.168.1.221
192.168.1.222
192.168.1.223
192.168.1.224
192.168.1.225

NOTE: do not press enter at the end of the last line. Otherwise your script will have problems at the end.

If your are doing this on scale you would be using a Python Automation Framework like Nornir. This gives you the benefit of an inventory, much like Ansible.

However, it’s still good to understand how to perform this task manually before jumping into other topics.

2. Backup Cisco Config with Python

Now we have established how to connect to multiple devices and can run basic commands, the next step is to be able to save that output.

One of the first tasks people usually take on when they get started with network automation is to take a backup of a configuration file. This Python script does just that.

3. Config Generator using Jinja2

4. IP Valid Checker

This simple Python script uses the ipaddress module and will validate if an entered IPv4 or IPv6 address is valid or not.

import os, ipaddress 

os.system('cls')

while True:
    ip = input('Enter IP Address: ')
    try: 
        print(ipaddress.ip_address(ip))
        print('IP Valid')
    except: 
        print:('-' *50)
        print('IP is not valid')
    finally: 
        if ip =='q':
           print('Script Finished')
           break