Using Python TextFSM to retrieve structured output from Cisco devices

Cisco’s lack of a robust API or the ability to return structured output from the CLI is a challenge when trying to automate networking configuration or retrieve telemetry information.

The Python module TextFSM attempts to resolve this deficiency by executing commands via the CLI and returning structured JSON formatted output.

Example Python script:

#!/usr/local/bin/python3

from netmiko import Netmiko
from getpass import getpass
import pprint

password = getpass()

output = []

net_connect = Netmiko(host="192.168.1.1", username="jemurray", password=password, device_type="cisco_ios")

net_connect.find_prompt()

output.append(net_connect.send_command("show version", use_textfsm=True))
output.append(net_connect.send_command("show interface GigabitEthernet1/0/1", use_textfsm=True))
output.append(net_connect.send_command("show interface GigabitEthernet1/0/12", use_textfsm=True))
output.append(net_connect.send_command("show vlan id 120", use_textfsm=True))


for i in output:
    pp = pprint.PrettyPrinter(indent=4)
    pp.pprint(i)

Returned output:

[email protected]:~/g/scripts $ ./structuredSwitchOuput.py
Password:
[   {   'config_register': '0x102',
        'hardware': ['WS-C3850-12S'],
        'hostname': 'LAB-3850-SW',
        'mac': ['00:56:2b:13:aa:bb'],
        'reload_reason': 'Power Failure or Unknown',
        'rommon': 'IOS-XE',
        'running_image': 'packages.conf',
        'serial': ['LABSERIALNUMBER'],
        'uptime': '1 year, 35 weeks, 5 days, 8 hours, 53 minutes',
        'version': '16.6.4'}]

[   {   'address': '0056.2b13.fc81',
        'bandwidth': '1000000 Kbit',
        'bia': '0056.2b13.fc81',
        'delay': '10 usec',
        'description': 'rd-51-wu-ml-0 Ten1/0/7  MANAGED',
        'duplex': 'Full-duplex',
        'encapsulation': 'ARPA',
        'hardware_type': 'Gigabit Ethernet',
        'input_errors': '0',
        'input_packets': '81953194',
        'input_rate': '1000',
        'interface': 'GigabitEthernet1/0/1',
        'ip_address': '',
        'last_input': '00:00:03',
        'last_output': '00:00:01',
        'last_output_hang': 'never',
        'link_status': 'up',
        'mtu': '1500',
        'output_errors': '0',
        'output_packets': '96787774',
        'output_rate': '7000',
        'protocol_status': 'up (connected)',
        'queue_strategy': 'fifo',
        'speed': '1000Mb/s'}]

[   {   'address': '0056.2b13.fc8c',
        'bandwidth': '1000000 Kbit',
        'bia': '0056.2b13.fc8c',
        'delay': '10 usec',
        'description': 'des BUILD NETWORK MANAGED',
        'duplex': 'Full-duplex',
        'encapsulation': 'ARPA',
        'hardware_type': 'Gigabit Ethernet',
        'input_errors': '0',
        'input_packets': '17238614',
        'input_rate': '0',
        'interface': 'GigabitEthernet1/0/12',
        'ip_address': '',
        'last_input': '1y32w',
        'last_output': '00:00:00',
        'last_output_hang': 'never',
        'link_status': 'up',
        'mtu': '1500',
        'output_errors': '0',
        'output_packets': '38493915',
        'output_rate': '0',
        'protocol_status': 'up (connected)',
        'queue_strategy': 'fifo',
        'speed': '1000Mb/s'}]

[   {   'interfaces': ['Gi1/0/1'],
        'name': 'VLAN0120',
        'status': 'active',
        'vlan_id': '120'}]

Git repo and more information here


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