Configuring basic system information

In this recipe, we will outline how we can configure basic system parameters on Cisco IOS devices, such as setting the hostname, DNS server, and NTP servers. Following the network setup that we outlined at the start of this chapter, we will configure the following information on all the Cisco IOS devices:

• DNS servers 172.20.1.250 and 172.20.1.251
• NTP server 172.20.1.17

Getting ready

An Ansible inventory file must be present, as well as the configuration for Ansible to connect to the Cisco IOS devices via SSH.

How to do it...

1. To the group_vars/network.yml file, add the following system parameters:

$ cat group_vars/network.yml
<-- Output Trimmed for brevity ------>
name_servers:
 - 172.20.1.250
 - 172.20.1.251
ntp_server: 172.20.1.17

2. Create a new playbook called pb_build_network.yml with the following information:

$ cat pb_build_network.yml
  ---
- name: "PLAY 1: Configure All Lan Switches"
  hosts: lan
  tags: lan
  tasks:
  - name: "Configure Hostname and Domain Name"
    ios_system:
      hostname: "{{ inventory_hostname }}"
      domain_name: "{{ domain_name }}"
      lookup_enabled: no
      name_servers: "{{ name_servers }}"
  - name: "Configure NTP"
    ios_ntp:
      server: "{{ ntp_server }}"
      logging: true
      state: present

How it works...

In the network.yml file, we define the name_servers variable as a list of DNS servers, and we also define the ntp_servers variable, which defines the NTP servers that we want to configure on the IOS devices. Defining these parameters in the network.yml file applies these variables to all the devices within the network group.

We create a playbook and the first play targets all the hosts in the lan group (this includes both access and core devices) and, within this play, we reference two tasks:

• ios_system: This sets the hostname and the DNS servers on the devices.
• ios_ntp: This configures the NTP on the IOS devices and enables logging for NTP events.

Both these modules are declarative Ansible modules in which we just identify the state pertaining to our infrastructure. Ansible converts this declaration into the necessary IOS commands. The modules retrieve the configuration of the devices and compare the current state with our intended state (to have DNS and NTP configured on them) and then, if the current state does not correspond to the intended state defined by these modules, Ansible will apply the needed configuration to the devices.

When we run these tasks on all the LAN devices, the following configuration is pushed to the devices:

!
 ip name-server 172.20.1.250 172.20.1.251
 no ip domain lookup
 ip domain name lab.net
 !
 ntp logging
 ntp server 172.20.1.17
 !

See also...

For more information regarding the ios_system and ios_ntp modules, as well as the different parameters supported by these modules, please consult the following URLs:

• https://docs.Ansible.com/Ansible/latest/modules/ios_system_module.html
• https://docs.Ansible.com/Ansible/latest/modules/ios_ntp_module.html