Ansible and Juniper Junos – Interfaces

Previously we had made our first incursions connecting an Ansible control node with a Juniper router. In this post, we’ll see how to retrieve information about the router interfaces, both layer 2 and layer 3, and configure new interfaces.

The official Ansible modules reference will be your main guide for any additional information.
https://docs.ansible.com/ansible/latest/modules/list_of_network_modules.html#junos

If you are interested on this subject, but don’t have access to physical gear, most of it should work on virtual appliances like vMX, vQFX, which you can operate on a stand-alone mode or on a network environment like GNS3 or EVE-NG.

Juniper vLabs will also give you an introduction to the Juniper platform.
https://jlabs.juniper.net/vlabs/portal/index.page

Layer 2 Interfaces

A basic layer 2 interface configuration in Junos looks like this:

ge-0/0/1 {
     description "L2 interface";
     speed 1g;
     unit 0 {
         family ethernet-switching {
             interface-mode access;
             vlan {
                 members vlan30;
             }
         }
     }
 }

This configuration can be written as an Ansible playbook like this:

- name: "Replace provided configuration with device configuration"
  junos_l2_interfaces:
    config:
      - name: ge-0/0/1
        access:
          vlan: v30
    state: merged

Currently, I do not have any EX series or QFX series to decomission and run tests against it, so stay tuned for any updates on this.

The official module documentation is on https://docs.ansible.com/ansible/latest/modules/junos_l2_interfaces_module.html.

Layer 3 Interfaces

A basic layer 3 interface configuration in Junos looks like this:

ge-0/0/1 {
     unit 0 {
         family inet {
             address 192.168.1.10/24;
         }
     }
 }

This configuration can be written as an Ansible playbook like the following, using the same format as the last post.

---
- hosts: all
  gather_facts: no

  tasks:

  - name: Config ge-0/0/1
    junos_l3_interfaces:
      config:
        - name: ge-0/0/1
          ipv4:
            - address: 192.168.1.10/24
      state: merged

Let’s run it and check the result.

$ ansible-playbook juniper.yml -i juniper-hosts.yml

PLAY [all] ********************************************************************************************************************

TASK [Config ge-0/0/1] ********************************************************************************************************
[WARNING]: Platform linux on host 192.168.15.220 is using the discovered Python interpreter at /usr/bin/python, but future
installation of another Python interpreter could change this. See
https://docs.ansible.com/ansible/2.9/reference_appendices/interpreter_discovery.html for more information.

changed: [192.168.15.220]

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

Did you noticed the changed output?
What about the configuration on the router now?

admin> show configuration interfaces
ge-0/0/1 {
    unit 0 {
        family inet {
            address 192.168.1.10/24;
        }
    }
}
fxp0 {
    unit 0 {
        family inet {
            address 192.168.15.220/24;
        }
        family inet6;
    }
}

That’s awesome! We just configured and IP address on ge-0/0/1.

How does Ansible knows what to replace, what to override, and what to delete?

If you take a closer look to the playbook, you will see a line with state: merged. This is a module parameter that specifies the state of the router configuration after the module finishes its job.

The possible values are:

• merged
• replaced
• overriden
• deleted

In fact, the module matches whatever configuration you build on its parameters, applies a configuration action, and commits the result.

The official module documentation is on https://docs.ansible.com/ansible/latest/modules/junos_l3_interfaces_module.html.