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Network automation with Ansible filters

Learn to use a Jinja2 plugin to handle network configurations in server-provisioning playbooks.
Black filter with light behind

Photo by Aravind V on Unsplash

Ansible uses the Jinja2 templating system to handle variables in YAML playbooks. As I explained in my previous articlefilters are a very powerful feature in Ansible that allow you to manipulate data in many different ways. One useful filtering example is network configuration.

There's a Jinja2 filter that's useful when working with a network and an IP address: ipaddr(). To use it, you need to make sure you have the netaddr Python package, which you can install using:

% python3 -m pip install netaddr

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Depending on the version of Python and Ansible, you may need to use pip3 to install the module. Just make sure that the Python and pip you use match what Ansible is using:

$ ansible --version | grep python
  ansible python module location = /usr/lib/python3.10/site-packages/ansible
  python version = 3.10.6 (main, Aug  2 2022, 00:00:00) [GCC 12.1.1 20220507 (Red Hat 12.1.1-1)]

$ which python

One last step before you can play with netaddr. If you're running an Ansible version greater than 2.9, you must install a collection called named ansible.utils. You can install it from Ansible Galaxy:

$ ansible-galaxy collection install ansible.utils
Starting galaxy collection install process
Process install dependency map
Starting collection install process
Downloading to /home/admin2/.ansible/tmp/ansible-local-9482ftgrtdax/tmpg_vgd4id/ansible-utils-2.6.1-o60tm43g
Installing 'ansible.utils:2.6.1' to '/home/admin2/.ansible/collections/ansible_collections/ansible/utils'
ansible.utils:2.6.1 was installed successfully

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Handle network and IP addresses

The following playbook showcases a mere fraction of the things you can do with this powerful plugin, but refer to the documentation here and here to see how much more is available.

- name: Handling network and IP addresses
  hosts: localhost
  gather_facts: false
      - ""
      - "10.0.300" 
      - ""
      - "fe80::100/10"
      - ""
    - name: Show information for network and ip
          - "IP................: {{ item }}"
          - "Is it a valid IP?.: {{ item | ansible.utils.ipaddr }}"
          - "Just the IP.......: {{ item | ansible.utils.ipaddr('address') }}"
          - "Is this a network?: {{ item | ansible.utils.ipaddr('net') }}"
      loop: "{{ my_ips }}"

Here is the resulting output:

$ ansible-playbook 04_ipaddr.yml 
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'

PLAY [Handling network and IP addresses] **************************************************************

TASK [Show information for network and ip] **************************************************************
ok: [localhost] => (item= => {
    "msg": [
        "Is it a valid IP?.:",
        "Just the IP.......:",
        "Is this a network?: "
ok: [localhost] => (item=10.0.300) => {
    "msg": [
        "IP................: 10.0.300",
        "Is it a valid IP?.: False",
        "Just the IP.......: False",
        "Is this a network?: False"
ok: [localhost] => (item= => {
    "msg": [
        "Is it a valid IP?.:",
        "Just the IP.......:",
        "Is this a network?: "
ok: [localhost] => (item=fe80::100/10) => {
    "msg": [
        "IP................: fe80::100/10",
        "Is it a valid IP?.: fe80::100/10",
        "Just the IP.......: fe80::100",
        "Is this a network?: "
ok: [localhost] => (item= => {
    "msg": [
        "Is it a valid IP?.:",
        "Just the IP.......: ",
        "Is this a network?:"

PLAY RECAP ********************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 

The playbook and output deserve some additional explanation.

First, I defined the list my_ips to contain some valid IPv4 and IPv6 addresses, one invalid address, and a network address.

Next, I used that information in a loop to show what the ipaddr plugin can tell about each item:

  • "IP" — This is just the original IP from my list.
  • "Is it a valid IP?" — If it is, the plugin shows the IP itself. Otherwise, it shows False.
  • "Just the IP" — Gives only the address without the subnet mask.
  • "Is this a network?" — If it is, it shows the network address. Otherwise, it is empty.

In this example, my goal is to display the results. If I use this filter to configure network devices, I could do something similar or assign the content to variables and use it in subsequent tasks, roles, or even Ansible templates.

Wrap up

The ipaddr plugin is very handy for network configurations in server-provisioning playbooks. It is even more necessary for configuring network devices, and as you can see in the full documentation, the plugin is prepared for IPv6.

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Note: An earlier version of this article referred to ansible.netcommon and it has been updated to use ansible.utils instead.

Check out these related articles on Enable Sysadmin

Topics:   Ansible   Automation   Networking  
Author’s photo

Roberto Nozaki

Roberto Nozaki [RHCSA/RHCE/RHCA]  is a Senior Consultant at Red Hat Canada where he specializes in IT automation with Ansible. More about me

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