Automating Network Devices with Ansible

Ansible is a great automation tool for system and network engineers, with Ansible we can automate small network to a large scale enterprise network. I have been using Ansible to automate both Aruba, and Cisco switches from my Fedora powered laptops for a couple of years. This article covers the requirements and executing a couple of playbooks.

Configuring Ansible

If Ansible is not installed, it can be installed using the command below

$ sudo dnf -y install ansible

Once installed, create a folder in your home directory or a directory of your preference and copy the ansible configuration file. For this demonstration, I will be using the following.

$ mkdir -pv /home/$USER/network_automation
$ sudo cp -v /etc/ansible.cfg /home/$USER/network_automation
$ cd /home/$USER/network_automation
$ sudo chown $USER:$USER ansible.cfg && chmod 0600 ansible.cfg

To prevent lengthy commands from failing, edit the ansible.cfg and append the following lines. We must add the persistent connection and set the desired time in seconds for the command_timeout as demonstrated below. A use case where this is useful is when you are performing backups of a network device that has a lengthy configuration.

$ vim ansible.cfg
[persistent_connection]
command_timeout = 300
connection_timeout = 30

Requirements

If SELinux is enabled, you will need to install SELinux binding, which is required when using the copy module.

# Install SELinux bindings
$ sudo dnf -y install python3-libselinux python3-libsemanage

Creating the inventory

The inventory holds the names of the network assets, and grouping of the assets are in square brackets [], below is a  sample inventory.

[site_a]
Core_A ansible_host=192.168.122.200
Distro_A ansible_host=192.168.122.201
Distro_B ansible_host=192.168.122.202

Playbook

Read Operations

Let us create a simple playbook to run a show command to read the configuration on a few switches.

  1 ---
  2 - name: Basic Playbook
  3   hosts: site_a
  4   connection: local
  5 
  6   tasks:
  7   - name: Get Interface Brief
  8     ios_command:
  9       commands:
 10         - show ip interface brief | e una
 11     register: interfaces
 12 
 13   - name: Print results
 14     debug:
 15       msg: "{{ interfaces.stdout[0] }}

The above images show the differences without and with the debug module respectively.

Let’s break the playbook into three blocks, starting with lines 1 to 4.

• The three dashes/hyphens starts the YAML document
• The hosts defines the hosts or host groups, multiple groups are comma-separated
• Connection defines the methodology to connect to the network devices. Another option is network_cli (recommended method) and will be used later in this article. See IOS Platform Options for more details.

Lines 6 to 11 starts the tasks, we will be using ios_command and ios_config. This play will execute the show command show ip interface brief | e una and save the output from the command into the interfaces variable, with the register key.

Lines 13 to 15, by default, when you execute a show command you will not see the output, though this is not used during automation. It is very useful for debugging; therefore, the debug module was used.

The below video shows the execution of the playbook. There are a couple of ways you can execute the playbook.

• Passing arguments to the command line, for example, include -u <username> -k to prompt for the remote user credentials

ansible-playbook -i inventory show_demo.yaml -u admin -k

• Include the credentials in the host or group vars

ansible-playbook -i inventory show_demo.yaml

Never store passwords in plain text. We recommend using SSH keys to authenticate SSH connections. Ansible supports ssh-agent to manage your SSH keys. If you must use passwords to authenticate SSH connections, we recommend encrypting them with Using Vault in Playbooks

If we want to save the output to a file, we will use the copy module as shown in the playbook below. In addition to using the copy module, we will include the backup_dir variable to specify the directory path.

---
- name: Get System Infomation
  hosts: site_a
  connection: network_cli
  gather_facts: no
  
  vars:
    backup_dir: /home/eramirez/dev/ansible/fedora_magazine
  
  tasks:
  - name: get system interfaces
    ios_command:
      commands:
        - show ip int br | e una
    register: interface
    
  - name: Save result to disk
    copy:
      content: "{{ interface.stdout[0] }}"
      dest: "{{ backup_dir }}/{{ inventory_hostname }}.txt"

To demonstrate the use of variables in the inventory, we will use plain text. This method Must not be used in production.

[site_a]
Core_A ansible_host=192.168.122.200
Distro_A ansible_host=192.168.122.201
Distro_B ansible_host=192.168.122.202
[all:vars]
ansible_connection=network_cli
ansible_network_os=ios
ansible_user=admin
ansible_password=fedora
ansible_become=yes
ansible_become_password=yes
ansible_become_method=enable 

Write Operations

Let us create a playbook to configure a couple of interfaces in all of the network devices in site_a. We will first take a backup of the current configuration of all devices in site_a. Lastly, we will save the configuration.

---
- name: Get System Infomation
  hosts: site_a
  connection: network_cli
  gather_facts: no
  
  vars:
    backup_dir: /home/eramirez/dev/ansible/fedora_magazine
  
  tasks:
  - name: Backup configs
    ios_config:
      backup: yes
      backup_options:
        filename: "{{ inventory_hostname }}_running_cfg.txt"
        dir_path: "{{ backup_dir }}"
    
  - name: get system interfaces
    ios_config:
      lines:
        - description Raspberry Pi
        - switchport mode access
        - switchport access vlan 100
        - spanning-tree portfast
        - logging event link-status
        - no shutdown
      parents: "{{ item }}"
    with_items:
      - interface FastEthernet1/12
      - interface FastEthernet1/13
      
  - name: Save switch configuration
    ios_config:
      save_when: modified

Before we execute the playbook, we will first validate the interface configuration. We will then run the playbook and confirm the changes as illustrated below.

Conclusion

This article is a basic introduction to whet your appetite that demonstrates how Ansible is used to manage network devices. Ansible is capable of automating a vast network, which includes MPLS routing and performing validation before executing the next task.