Getting started with Network Automation using Python and Netmiko

Keen to get started on my automation journey, I struggled for a long time with telnet libraries like telnetlib and even resorted to dropping into an SSH process and scraping output via pexpect. To say it was cumbersome and error-prone is an understatement. I eventually gave up and went back to CLI bashing and using Kiwi / Solarwinds Cattools for delivering bulk changes.

A couple of weeks ago however I made a discovery, somebody much smarter than I am figured out a clean and reliable way to connect to network devices and return output. The good news is they kindly built a Python library to make life much easier for the rest of us. It’s not all about screen scraping output either, this library does a great job of delivering configuration changes as well.

Netmiko extends Paramiko (a Python library for managing SSH connections) by adding support for network devices and is written by Kirk Byers. As with all good open source projects, source code can be checked out from GitHub, or installed easily using Python’s pip installer.

I opted for the pip install on OSX, which is incredibly simple :

$pip install netmiko
Collecting netmiko
  Downloading netmiko-0.2.5-py2.py3-none-any.whl
Installing collected packages: netmiko
Successfully installed netmiko-0.2.5

There are several ways to install pip on OSX, some examples can be found on StackExchange (https://stackoverflow.com/questions/17271319/installing-pip-on-mac-os-x).

To get started with a basic example, load up the Python interpreter and import the Netmiko libary :

$python
Python 2.7.10 (v2.7.10:15c95b7d81dc, May 23 2015, 09:33:12)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from netmiko import ConnectHandler

From here we can easily connect to a Cisco IOS device (or Juniper Junos, Dell Force10, Fortinet etc) and collect some basic DSL line statistics :

router = {
'device_type': 'cisco_ios',
'ip': '1.2.3.4',
'username': 'USERNAME',
'password': 'PASSWORD',
'port' : 22, # optional, defaults to 22
'secret': 'ENABLE', # optional, defaults to ''
'verbose': True, # optional, defaults to True
}

net_connect = ConnectHandler(**router)

output = net_connect.send_command('show controllers vdsl 0')
output = output.split('\n')
#output is returned as a single string, so let's split this into lines in a list for iteration later

for line in output:
    if '(kbps)' in line:
    speed = line
    print (line,'\n')
    #for debugging purposes, let us know when we see the (kbps) line

If we separate whitespace on the line we’ve found, we can locate the upstream and downstream speeds :

speed = speed.split(' ')
downstream = str(speed[19]) #list entry 19 = downstream speed
upstream = str(speed[37]) #list entry 37 = upstream speed
print ("bandwidth",upstream)
print ("bandwidth receive",downstream)

Output from this script :

$ python3 dsl.py
SSH connection established to 1.2.3.4:22
Interactive SSH session established
parsing output..

Speed (kbps): 0 4347 0 760

bandwidth 760
bandwidth receive 4347

There are probably neater and more Pythonic ways to achieve this, but I’m just starting out on my journey and I’m sure my code will improve over time.

That aside, it would be trivial take these variables and use them to generate some configuration, dropping them back onto the relevant dialer interface using the net_connect.send_config_set method, helping monitoring tools like Solarwinds Orion report the correct interface speeds for DSL interfaces, rather than the defaults we usually see. I’ll save that for my next post though..

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