Ansible for Networking

Ansible is an open-source automation framework that uses YAML playbooks to define automation tasks. It is agentless — it connects to devices over SSH or APIs without requiring any software to be installed on the managed devices. This makes it ideal for network automation, where you cannot install agents on routers and switches.

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Why Ansible for Networking?

Feature	Benefit for Network Engineers
Agentless	No software to install on network devices
YAML-based	Human-readable, no programming required
Idempotent	Safe to run repeatedly without side effects
Multi-vendor	Modules for Cisco, Arista, Juniper, Palo Alto, and more
Community	Thousands of modules and roles on Ansible Galaxy
Extensible	Write custom modules in Python
Version control	Playbooks stored in Git like any other code

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Ansible Architecture

┌─────────────────────────────────────────┐
│           Control Node                  │
│  (Linux/macOS with Ansible installed)   │
│                                         │
│  inventory.yaml    playbook.yaml        │
│  group_vars/       host_vars/           │
│  roles/            templates/           │
└────────────┬────────────────────────────┘
             │
      SSH / NETCONF / API
             │
     ┌───────┼───────────┐
     ▼       ▼           ▼
  [Router] [Switch] [Firewall]
  Managed   Managed   Managed
  Nodes     Nodes     Nodes

Component	Description
Control node	The machine where Ansible runs (Linux or macOS)
Managed nodes	The devices being automated (routers, switches, firewalls)
Inventory	List of managed devices and their variables
Playbook	YAML file defining tasks to execute
Module	A unit of work (e.g., cisco.ios.ios_config)
Role	Reusable, structured set of tasks
Collection	Package of modules, roles, and plugins

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Installation

# Install Ansible
pip install ansible

# Install network collections
ansible-galaxy collection install cisco.ios
ansible-galaxy collection install arista.eos
ansible-galaxy collection install junipernetworks.junos

---

Inventory

The inventory defines which devices to manage:

# inventory.yaml
all:
  children:
    routers:
      hosts:
        core-rtr-01:
          ansible_host: 192.168.1.1
        core-rtr-02:
          ansible_host: 192.168.1.2
      vars:
        ansible_network_os: cisco.ios.ios
        ansible_connection: ansible.netcommon.network_cli
        ansible_user: admin
        ansible_password: secret
        ansible_become: true
        ansible_become_method: enable
        ansible_become_password: enable_secret

    switches:
      hosts:
        access-sw-01:
          ansible_host: 192.168.1.10
        access-sw-02:
          ansible_host: 192.168.1.11
      vars:
        ansible_network_os: arista.eos.eos
        ansible_connection: ansible.netcommon.network_cli
        ansible_user: admin
        ansible_password: secret

---

Playbooks

A playbook defines a list of tasks to run against inventory hosts:

Show Command Playbook

# show_version.yaml
---
- name: Gather device information
  hosts: routers
  gather_facts: false

  tasks:
    - name: Run show version
      cisco.ios.ios_command:
        commands:
          - show version
      register: version_output

    - name: Display output
      ansible.builtin.debug:
        msg: "{{ version_output.stdout_lines[0] }}"

# Run the playbook
ansible-playbook -i inventory.yaml show_version.yaml

Configuration Playbook

# configure_ntp.yaml
---
- name: Configure NTP on all routers
  hosts: routers
  gather_facts: false

  tasks:
    - name: Set NTP servers
      cisco.ios.ios_config:
        lines:
          - ntp server 10.0.0.50
          - ntp server 10.0.0.51
        save_when: modified