# DevNet Lab 15 -- Use Ansible to Back Up and Configure a c8000v Router
[toc]
---
### Scenario
In this lab, you will explore the basics of using Ansible to automate backup and interface addressing tasks. First, you will configure Ansible in your **DevNet** virtual machine. Next, you will use Ansible to connect to the virtual router and back up its configuration. Then you will configure this virtual router with IPv6 addressing and discover that *idempotence in automation comes at a significant cost*.
### Objectives
After completing the manipulation steps in this document, you will be able to:
- Configure Ansible in a DevNet virtual machine Environment
- Establish SSH connectivity between the DevNet VM and a virtual router
- Automate router configuration tasks using Ansible playbooks
- Apply Ansible to configure IPv6 addressing on a router interface
- Understand and implement idempotency in Ansible playbooks
- Refactor playbook tasks to achieve better idempotency
## Part 1: Configure Ansible on the Devnet virtual machine
In this part, you will configure Ansible to run from a specific directory.
### Step 1: Create the Ansible directory and configuration file
1. Ensure the `~/labs/lab15` directory exist and navigate to this folder
```bash
mkdir -p ~/labs/lab15 && cd ~/labs/lab15
```
2. Install **ansible** Python virtual environement
There are two main ways to set up a new Ansible workspace. Packages and Python virtual environments are both viable options. Here we choose to install Ansible in a Python virtual environment to take advantage of the latest release.
We start by creating a `requirements.txt` file.
```bash
cat << EOF > requirements.txt
ansible
ansible-lint
ansible-pylibssh
netaddr
EOF
```
Then we install the tools in a virtual environment called `ansible`.
```bash
python3 -m venv ansible
source ./ansible/bin/activate
pip3 install -r requirements.txt
```
3. Create a new `ansible.cfg` file in the `lab15` directory from the shell prompt
```bash
cat << 'EOF' > ansible.cfg
# config file for Lab 14 virtual router management
[defaults]
# Use inventory/ folder files as source
inventory=inventory/
host_key_checking = False # Don't worry about RSA Fingerprints
retry_files_enabled = False # Do not create them
deprecation_warnings = False # Do not show warnings
interpreter_python = /usr/bin/python3
[inventory]
enable_plugins = auto, host_list, yaml, ini, toml, script
[persistent_connection]
command_timeout=100
connect_timeout=100
connect_retry_timeout=100
ssh_type = libssh
EOF
```
4. Ensure that all necessary libraries and collections are up to date.
Update Cisco Ansible collection to the lastest version
```bash
ansible-galaxy collection install -f cisco.ios --upgrade
```
The local collections have priority over the system collection.
```bash
ansible-galaxy collection list
```
```bash=
# /home/etu/.ansible/collections/ansible_collections
Collection Version
---------------------------------------- -------
cisco.ios 9.1.1
```
5. Create the `inventory` directory
```bash
mkdir ~/labs/lab15/inventory
```
The contents of this directory will later be supplemented by the virtual router's connection parameters.
### Step 2: Check SSH access from Devnet VM to virtual router
We start with a shell test connection before to set the configuration for **ansible**.
Be sure the virtual router is already up and running. If it's not the case, refer to [DevNet Lab 13 – Run the Cisco IOS-XE router VM](https://md.inetdoc.net/s/jeuIbS6bK)
:::warning
One more time, be sure to change placeholders to match your resource allocation.
:::
Here is a sample declaration file for programming hypervisor switch ports:
```yaml=
ovs:
switches:
- name: dsw-host
ports:
- name: tapXX7 # management interface connection
type: OVSPort
vlan_mode: access
tag: VVV # out-of-band VLAN id
- name: tapXX8 # in-band interface connection
type: OVSPort
vlan_mode: trunk
trunks: [100, 101, 102]
- name: tapXX9 # unused interface in this lab
type: OVSPort
vlan_mode: access
tag: 999
```
From the hypervisor shell, apply this switch configuration with the following command:
```bash
switch-conf.py lab15-switch.yaml
```
Return to the DevNet development virtual machine shell, start an initial SSH connection to the virtual router, and accept the router's fingerprint.
```bash
ssh etu@fe80::faad:caff:fefe:XXX%enp0s1
```
```bash=
The authenticity of host 'fe80::faad:caff:fefe:XXX%enp0s1 (fe80::faad:caff:fefe:XXX%enp0s1)' can't be established.
RSA key fingerprint is SHA256:e+oyegX4BzzQSKNVz7vjoi8psHTxUjIw/rc/44Y8tHY.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'fe80::faad:caff:fefe:2%enp0s1' (RSA) to the list of known hosts.
(etu@fe80::faad:caff:fefe:XXX%enp0s1) Password:
rtrXXX#
```
:::success
This SSH connection uses the default user account created by the Zero Touch Programming (ZTP) Python script. This initial router configuration only occurs when the router management interface is connected to the out-of-band auto-addressing VLAN.
:::
### Step 3: Create a new Ansible vault file
1. Create a new vault file called `.lab_passwd.yml` and enter the unique vault password which will be used for all users passwords to be stored.
```bash
ansible-vault create $HOME/.lab_passwd.yml
```
```bash=
New Vault password:
Confirm New Vault password:
```
This will open the default editor which is defined by the `$EDITOR` environment variable.
There we enter a variable name which will designate the password for Web server VM user account.
```bash
ansible_user_passwd: 4n51bl3
```
2. Create the **ansible_user** account on the IOS XE system of the C8000v virtual router
From the default user account SSH connection already opened, add a new user account with the highest privilege level and the same password as the one chosen for the ansible vault.
```
rtrXXX#conf terminal
Enter configuration commands, one per line. End with CNTL/Z.
rtrXXX(config)#user ansible_user privilege 15 secret 4n51bl3
rtrXXX(config)#^Z
rtrXXX#copy run start
Destination filename [startup-config]?
Building configuration...
[OK]
```
3. Close the default user SSH connection and open a new one with the identity **ansible_user** and list the IPv6 addresses of this router to fill the inventory file.
- First, complete your SSH config file in order to avoid identity conflicts on Local Link IPv6 addresses
```bash=
cat << EOF >> $HOME/.ssh/config
Host fe80::*
CheckHostIP no
StrictHostKeyChecking no
UserKnownHostsFile=/dev/null
EOF
```
- Second, open the new SSH conection
```
ssh ansible_user@fe80::faad:caff:fefe:XXX%enp0s1
Warning: Permanently added 'fe80::faad:caff:fefe:2%enp0s1' (RSA) to the list of known hosts.
(ansible_user@fe80::faad:caff:fefe:2%enp0s1) Password:
rtrXXX#sh users
Line User Host(s) Idle Location
*434 vty 0 ansible_us idle 00:00:00 FE80::BAAD:CAFF:FEFE:0
Interface User Mode Idle Peer Address
rtrXXX#sh ipv6 int br GigabitEthernet 1
GigabitEthernet1 [up/up]
FE80::FAAD:CAFF:FEFE:2
2001:678:3FC:1C:FAAD:CAFF:FEFE:2
```
In the screenshot above, we have a choice of 2 IPv6 addresses: the local link address or the GUA address.
:::info
It is good practice to have the DevNet VM and the out-of-band router interface on the same VLAN.
This is why we chose to use the Local Link IPv6 address in the inventory file.
:::
### Step 4: Create the Ansible inventory file
Ansible uses an inventory file called hosts, which contains device information used by Ansible playbooks.
In this lab, you will be running Ansible from the git project's lab directory. Therefore, you will need separate hosts and ansible.cfg files for each lab.
:::info
The terms "hosts file" and "inventory file" are synonymous and are used interchangeably throughout the Ansible labs.
:::
The Ansible inventory file defines the devices and groups of devices used by the Ansible playbook. The file can be in one of many formats, including YAML and INI, depending on your Ansible environment.
The inventory file can list devices by IP address or fully qualified domain name (FQDN), and can also include host-specific parameters.
Create the `hosts.yml` inventory file in the `inventory` directory, add the following content to the file and save it. Any `XXX` tags must be edited to identify your own C8000v virtual router instance.
```bash
cat << EOF > inventory/hosts.yml
ios:
hosts:
rtrXXX:
ansible_host: fe80::faad:caff:fefe:XXX%enp0s1
ansible_port: 2222
vars:
ansible_ssh_user: ansible_user
ansible_ssh_pass: "{{ ansible_user_passwd }}"
ansible_connection: network_cli
ansible_network_os: ios
all:
children:
ios:
EOF
```
The `hosts.yml` file starts with the **\[ios\]** section. This section lists aliases for a set of devices. Here we have a single alias: **rtrXXX**. An host group is used in the Ansible playbook to refer to a device specified by the **ansible_host** and **ansible_port** variables.
Within the **\[ios\]** section, the `hosts.yml` file specifies a set of variables that the Ansible playbook will use to access the device. These are the SSH credentials that Ansible needs to securely access the c8000v virtual router.
**ansible_ssh_user**
: Username used to connect to the remote device. Without this, the user that is running the ansible playbook would be used.
**ansible_ssh_pass**
: Password for **ansible_ssh_user**. If omitted, the SSH key would be used.
**ansible_connection**
: Specifies the library to use to connect to the device.
**ansible_network_os**:
: Specifies the operating system used on the endpoint.
### Step 5: Verify the Ansible configuration and check router access.
1. Use the **ansible \--version** command to display version information.
```bash
ansible --version
```
```bash=
ansible [core 2.18.3]
config file = /home/etu/labs/lab15/ansible.cfg
configured module search path = ['/home/etu/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
ansible python module location = /home/etu/labs/lab15/ansible/lib/python3.12/site-packages/ansible
ansible collection location = /home/etu/.ansible/collections:/usr/share/ansible/collections
executable location = /home/etu/labs/lab15/ansible/bin/ansible
python version = 3.12.3 (main, Feb 4 2025, 14:48:35) [GCC 13.3.0] (/home/etu/labs/lab15/ansible/bin/python3)
jinja version = 3.1.5
libyaml = True
```
2. Parse your own ansible.cfg file.
Now, you need to edit your `ansible.cfg` file to look at the location of your `hosts.yml` inventory file.
Open the `ansible.cfg` file and search lines referring to inventory.
```bash
grep -A2 inventory ansible.cfg
```
```bash=
# Use inventory/ folder files as source
inventory=inventory/
host_key_checking = False # Don't worry about RSA Fingerprints
retry_files_enabled = False # Do not create them
--
[inventory]
enable_plugins = auto, host_list, yaml, ini, toml, script
[persistent_connection]
```
As in Python, the \# is used for comments within the **ansible.cfg** file.
Comments cannot follow an entry. Ansible treats the \# and subsequent comment as part of the filename. Therefore, in these cases, the \# comment must be on a separate line.
However, variables can have a comment on the same line, as shown for **host_key_checking** and **retry_files_enabled**.
The `ansible.cfg` file tells Ansible where to find the inventory file and sets certain default parameters. The information you put in your `ansible.cfg` file is:
**inventory=inventory/**
: All your inventory files are in the **inventory** directory.
**host_key_checking = False**
: There are no SSH keys set up in the local development environment. You have set **host_key_checking** to **False**, which is the default. In a production network, **host_key_checking** would be set to **True**.
**retry_files_enabled = False**
: If Ansible has troubles running playbooks for a host, it will output the host name to a file in the current directory ending in **retry**. To avoid clutter, it is common to disable this setting.
### Step 6: Ansible configuration files summary
In this part you have configured Ansible to run in the lab directory.
In this lab you will need an `ansible.cfg` file in your `ansible` directory and an inventory file `hosts.yml` in the `inventory` directory.
- You edited the **hosts** file to contain login and IP address information for the virtual router
- You edited the **ansible.cfg** file to use the local hosts file as the inventory file
In the next part, you will create a playbook to tell Ansible what to do.
The inventory status can be checked using the **ansible-inventory** command:
```bash
ansible-inventory --yaml --list
```
```bash=
all:
children:
ios:
hosts:
rtrXXX:
ansible_connection: network_cli
ansible_host: fe80::faad:caff:fefe:XXX%enp0s1
ansible_network_os: ios
ansible_port: 2222
ansible_ssh_pass: "{{ ansible_user_passwd }}"
ansible_ssh_user: ansible_user
```
The connection to the router device can be checked using the Ansible **ping module**:
```bash
ansible -m ping all --ask-vault-pass --extra-vars '@$HOME/.lab_passwd.yml'
```
```bash=
Vault password:
rtrXXX | SUCCESS => {
"changed": false,
"ping": "pong"
}
```
## Part 2: Use Ansible to back up router configuration
In this part, you will create an Ansible playbook that automates the process of backing up the router configuration. Playbooks are at the heart of Ansible. Whenever you want Ansible to retrieve information or perform an action on a device or group of devices, you run a playbook to get the job done.
An Ansible playbook is a YAML file containing one or more plays. Each play is a collection of tasks.
**play**
: A matching set of tasks to a device or group of devices.
**task**
: A single action that references a **module** to be executed along with any input arguments and actions. These tasks can be simple or complex, depending on the need for permissions, the order in which the tasks are executed, and so on.
A playbook may also contain **roles**. A role is a mechanism for splitting a playbook into multiple components or files, simplifying the playbook and making it easier to reuse. For example, the **common** role is used to store tasks that can be used in all of your playbooks.
Roles are beyond the scope of this lab.
The Ansible YAML playbook includes **objects**, **lists** and **modules**.
- A YAML object consists of one or more key-value pairs. Key-value pairs are separated by a colon without quotation marks, for example **hosts: Router**.
- An object can contain other objects, such as a list. YAML uses lists or arrays. A hyphen "-" is used for each element in the list.
- Ansible ships with a set of modules (called the module library) that can be run directly on remote hosts or through playbooks.
An example is the **ios_command** module, which is used to send commands to an IOS device and return the results. Each task typically consists of one or more Ansible modules.
The **ansible-playbook** command uses parameters to specify
- The vault file that contains the credentials to decrypt to connect to the user account specified in the inventory file.
- The playbook you want to run **backup_router_playbook.yml**.
### Step 1: Create your Ansible playbook.
The Ansible playbook is a YAML file. Make sure you use the correct YAML indentation. Every space and hyphen is important. You may lose some formatting if you copy and paste the code in this lab.
1. Create a new file in the `ansible` directory with the following name: **backup_router_playbook.yml**
2. Add the following information to the file.
```yaml=
# The purpose of this playbook is to automatically back up the running
# configuration of a Cisco router.
---
- name: AUTOMATIC BACKUP OF ROUTER CONFIGURATION
hosts: ios
tasks:
- name: BACKUP RUNNING CONFIG
cisco.ios.ios_config:
backup: true
...
```
### Step 2: Examine your Ansible playbook.
The playbook you have created contains one play with one task. The following is an explanation of your playbook:
\-\--
: This is at the beginning of every YAML file and tells YAML that this is a separate document. Each file can contain several documents, separated by \-\--.
name:
: This is the name of the play.
hosts: ios
: This is the alias previously configured in the `hosts.yml` file. By referencing this alias in your playbook, the playbook can use any parameters associated with this inventory file entry, including the IP address of the devices.
tasks:
: This keyword specifies one or more tasks to perform.
The task is to backup the router configuration.
cisco.ios.ios_config:
: This is an Ansible **module** that is used to manage an IOS device configuration. The **ios_config** module belongs to the **cisco.ios** collection.
:::info
In the Linux terminal, you can use the **ansible-doc** *module_name* command to view the manual pages for any **module** and the parameters associated with that module. (e.g. **ansible-doc cisco.ios.ios_command or ansible-doc cisco.ios.ios_config**).
:::
backup:
: This parameter is associated with the **ios_config** module. It is used to list IOS commands in the playbook that are to send to the remote IOS device. The resulting command output is returned.
### Step 3: Run the Ansible backup Playbook.
1. In Part 1, you started the virtual VM. Ping it to verify you can reach it.
```bash
ping -c2 fe80::faad:caff:fefe:XXX%enp0s1
```
```bash=
PING fe80::faad:caff:fefe:XXX%enp0s1(fe80::faad:caff:fefe:XXX%enp0s1) 56 data bytes
64 bytes from fe80::faad:caff:fefe:XXX%enp0s1: icmp_seq=1 ttl=64 time=1.63 ms
64 bytes from fe80::faad:caff:fefe:XXX%enp0s1: icmp_seq=2 ttl=64 time=0.939 ms
--- fe80::faad:caff:fefe:XXX%enp0s1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 0.939/1.282/1.625/0.343 ms
```
2. Check if ansible has access to this router through its configuration file and inventory. The router hostname rtrXXX has to point on your own router in the **inventory** file.
```bash
ansible -m ping all --ask-vault-pass --extra-vars '@$HOME/.lab_passwd.yml'
Vault password:
```
```bash=
rtrXXX | SUCCESS => {
"changed": false,
"ping": "pong"
}
```
3. Now you can run the Ansible playbook using the **ansible-playbook** command:
```bash
ansible-playbook backup_router_playbook.yml --ask-vault-pass --extra-vars '@$HOME/.lab_passwd.yml'
Vault password:
```
```bash=
PLAY [AUTOMATIC BACKUP OF ROUTER CONFIGURATION] ***************************************
TASK [Gathering Facts] ****************************************************************
ok: [rtrXXX]
TASK [BACKUP RUNNING CONFIG] **********************************************************
changed: [rtrXXX]
PLAY RECAP ****************************************************************************
rtrXXX : ok=2 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
```
The **PLAY RECAP** should display **ok=2 changed=1** indicating a successful playbook execution.
If your Ansible playbook fails, some of the things to check in your playbook are:
- Make sure your `hosts.yml` and `ansible.cfg` files are correct.
- Make sure the YAML indentation is correct.
- Make sure your IOS command is correct.
- Check all the Ansible playbook syntax.
- Verify you can ping the C8000v.
If you continue to have problems:
- Check the inventory file content with the **ansible-inventory** command:
```bash
ansible-inventory --yaml --list
```
```yaml=
all:
children:
ios:
hosts:
rtrXXX:
ansible_connection: network_cli
ansible_host: fe80::faad:caff:fefe:XXX%enp0s1
ansible_network_os: ios
ansible_port: 2222
ansible_ssh_pass: "{{ ansible_user_passwd }}"
ansible_ssh_user: ansible_user
```
- Check your playbook syntax with the **ansible-lint** command:
```bash
ansible-lint router_config_playbook.yml
```
```
Passed: 0 failure(s), 0 warning(s) on 1 files. Last profile that met the validation criteria was 'production'.
```
The command results will show you the lines where there is a syntax error.
### Step 4: Verify the backup file has been created.
List files in the `backup` folder and open the most recent file. You can also use the **head** command to print the first lines of the backup file. You now have a backup of the router configuration.
```bash
ls -A backup
rtrXXX_config.2024-02-17@09:16:51
```
```bash
head -n 20 backup/rtrXXX_config.2024-02-17@09\:16\:51
```
```bash=
Building configuration...
Current configuration : 7172 bytes
!
! Last configuration change at 08:38:06 WEST Sat Feb 17 2024 by etu
! NVRAM config last updated at 08:46:09 WEST Sat Feb 17 2024 by ansible_user
!
version 17.13
service timestamps debug datetime msec
service timestamps log datetime localtime show-timezone
platform qfp utilization monitor load 80
platform punt-keepalive disable-kernel-core
platform sslvpn use-pd
platform console serial
!
hostname rtrXXX
!
boot-start-marker
boot-end-marker
!
```
## Part 3: Use Ansible to configure a router trunk interface
In this Part, you will create another Ansible playbook to configure IPv6 addressing on the C8000v router.
### Step 1: Create a new playbook.
1. Create a subdirectory named `host_vars` which will store variables of any device named in the inventory
```bash
mkdir host_vars
mkdir: created directory 'host_vars'
```
2. Create a new YAML file in the `host_vars` directory with the device name: `rtrXXX.yml`
```yaml=
---
rtr_id: XXX
# The IPv6 addresses are calculated by concatenating the following elements:
# the global prefix, the VLAN ID, the router ID as the interface ID, and the mask.
# For instance, the IPv6 address for VLAN 100 on router 7 is 2001:678:3fc:64::XXX/64.
ipv6_prefix: "2001:678:3fc:"
ipv6_intf_id: "{{ '%x' % rtr_id }}"
ipv6_mask: 64
# The main parent interface is GigabitEthernet2.
# The subinterfaces are created by appending the VLAN ID to the main interface.
# For instance, the subinterface for VLAN 100 is GigabitEthernet2.100.
interface:
type: GigabitEthernet
id: 2
vlans:
- name: red
id: 100
desc: RED VLAN SUBINTERFACE
- name: purple
id: 101
desc: PURPLE VLAN SUBINTERFACE
- name: blue
id: 102
desc: BLUE VLAN SUBINTERFACE
```
:::warning
Note that the keyword `interface:` is singular. It should be plural. For simplicity, we decided to limit the scope of the playbook to a single interface.
:::
3. Create a new file named `router_config_playbook.yml` in your lab directory, and add the following tasks to the file. Make sure you use the proper YAML indentation. Every space and dash is significant.
```yaml=
# The purpose of this playbook is to configure IPv6 addresses on subinterfaces
# of a Cisco router.
#
# 1. Calculate IPv6 addresses for each VLAN
# 2. Display the calculated IPv6 addresses, networks, and gateways
# 3. Configure the main parent interface
# 4. Configure sub-interfaces with dot1Q encapsulation, IPv6 addresses, and additional settings
# 5. Save the output of the IPv6 interface brief
# 6. Test reachability to the gateway address of each VLAN
# 7. Save the results of the reachability test
---
- name: VLAN SUBINTERFACES CONFIGURATION
hosts: all
tasks:
- name: CALCULATE IPv6 ADDRESSES
ansible.builtin.set_fact:
calculated_vlans: >
{{
calculated_vlans | default([]) +
[
item | combine(
{
'addr': ipv6_prefix ~
('%x' % item.id) ~
'::' ~
ipv6_intf_id ~
'/' ~
ipv6_mask
}
)
]
}}
loop: "{{ interface.vlans }}"
loop_control:
label: "{{ item.name }}"
- name: VARS ANALYSIS
ansible.builtin.debug:
msg:
- "vlan: {{ item.id }} --> address: {{ item.addr }}"
- "Network: {{ item.addr | ipv6 | ipaddr('network') }}/{{ item.addr | ipv6 | ipaddr('prefix') }}"
- "Gateway: {{ item.addr | ipv6 | ipaddr('1') }}"
loop: "{{ calculated_vlans }}"
- name: MAIN PARENT INTERFACE CONFIG
cisco.ios.ios_interfaces:
config:
- name: "{{ interface.type }}{{ interface.id }}"
description: IPV6 ANSIBLE PLAYBOOK CONFIGURATION
enabled: true
- name: SUB INTERFACES CONFIG
cisco.ios.ios_config:
lines:
- description {{ item.desc }}
- encapsulation dot1Q {{ item.id }}
- ipv6 address {{ item.addr }}
- ipv6 enable
- ipv6 nd ra suppress all
parents:
- interface {{ interface.type }}{{ interface.id }}.{{ item.id }}
match: exact
replace: block
with_items: "{{ calculated_vlans }}"
- name: SHOW IPv6 INTERFACE BRIEF
cisco.ios.ios_command:
commands:
- show ipv6 interface brief
register: output
- name: ENSURE TRACE DIRECTORY EXISTS
delegate_to: localhost
ansible.builtin.file:
path: trace
state: directory
mode: "0755"
- name: SAVE OUTPUT
ansible.builtin.copy:
content: "{{ output.stdout[0] }}"
dest: "trace/ipv6_int_brief_{{ inventory_hostname }}.txt"
mode: "0644"
- name: REACHABILITY TEST
cisco.ios.ios_ping:
dest: "{{ item.addr | ipv6 | ipaddr('1') | ipaddr('address') }}"
afi: ipv6
loop: "{{ calculated_vlans }}"
register: ping_results
- name: SAVE PING RESULTS
delegate_to: localhost
ansible.builtin.copy:
content: "{{ ping_results.results | to_nice_json }}"
dest: "trace/ipv6_ping_{{ inventory_hostname }}.txt"
mode: "0644"
```
### Step 2: Examine the Ansible playbook.
The main purpose of this playbook is to illustrate variable formatting and calculations. A set of VLAN identifiers is defined from the contents of the `host_vars/rtrXXX.yml` file. Then IPv6 subinterface addresses are calculated using a combination of:
- The prefix stands for the network part
- The VLAN id stands for the subnetwork part
- The router id stands for the host part
Note that we only need to change the router and VLAN identifiers to have all the IPv6 addresses automatically calculated.
Now, as we look at the contents of the `router_config_playbook.yml` file and what it does, here is a brief description of the elements used:
CALCULATE IPv6 ADDRESSES
: Iteratively builds a list of enriched VLAN objects by adding a calculated IPv6 address to each VLAN entry using the hexadecimal VLAN ID in the network portion and the router ID in the host portion, following a standard IPv6 address format with prefix and mask.
VARS ANALYSIS
: Use the **debug** module to view the calculation results as a detailed network address plan.
MAIN PARENT INTERFACE CONFIG
: Use the **ios_interfaces** module to enable the parent network interface and set its description.
SUB INTERFACES CONFIG
: Use the **ios_config** module to send line-by-line configuration instructions for each VLAN subinterface. This way of configuring network interfaces is useful when using commands that are not provided by the Ansible libraries. The downside here is that we lose idempotency and a warning is sent each time the playbook is run.
You can use the `ansible-doc cisco.ios.ios_config` command to see the details for the **parents** and **match** parameters used in this playbook.
SHOW IPv6 INTERFACE BRIEF
: Use the **ios_command** module to send the **show ipv6 interface brief** command. The output of the command is registered in an Ansible variable called **output**.
ENSURE TRACE DIRECTORY EXISTS
: Creates the `trace` directory in the DevNet lab tree if necessary.
SAVE OUTPUT
: Use the **copy** module to save the contents of the **outpout** variable to a file located in the `trace` directory on the Devnet VM.
REACHABILITY TEST
: Use the **ios_ping** module to send ICMPv6 requests to the network gateway of each subinterface VLAN.
### Step 3: Execute the Ansible playbook to set up IPv6 addressing on the virtual router
Now you can run the Ansible playbook with the `ansible-playbook` command. The **-vvv** verbose option can be added to display the tasks being performed in the playbook.
:::warning
Do not forget to replace the **rtr_id** value in the `host_vars/rtrXXX.yaml` with **your own** out of band **tap interface number!**.
This is mandatory in order to avoid duplicate addresses on different virtual routers.
:::
```bash
ansible-playbook router_config_playbook.yml --ask-vault-pass --extra-vars '@$HOME/.lab_passwd.yml'
Vault password:
```
```bash=
PLAY [VLAN SUBINTERFACES CONFIGURATION] *********************************************************
TASK [Gathering Facts] **************************************************************************
ok: [rtrXXX]
TASK [CALCULATE IPv6 ADDRESSES] *****************************************************************
ok: [rtrXXX] => (item=red)
ok: [rtrXXX] => (item=purple)
ok: [rtrXXX] => (item=blue)
TASK [VARS ANALYSIS] ****************************************************************************
ok: [rtrXXX] => (item={'name': 'red', 'id': 100, 'desc': 'RED VLAN SUBINTERFACE', 'addr': '2001:678:3fc:64::XXX/64'}) => {
"msg": [
"vlan: 100 --> address: 2001:678:3fc:64::XXX/64",
"Network: 2001:678:3fc:64::/64",
"Gateway: 2001:678:3fc:64::1/64"
]
}
ok: [rtrXXX] => (item={'name': 'purple', 'id': 101, 'desc': 'PURPLE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:65::XXX/64'}) => {
"msg": [
"vlan: 101 --> address: 2001:678:3fc:65::XXX/64",
"Network: 2001:678:3fc:65::/64",
"Gateway: 2001:678:3fc:65::1/64"
]
}
ok: [rtrXXX] => (item={'name': 'blue', 'id': 102, 'desc': 'BLUE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:66::XXX/64'}) => {
"msg": [
"vlan: 102 --> address: 2001:678:3fc:66::XXX/64",
"Network: 2001:678:3fc:66::/64",
"Gateway: 2001:678:3fc:66::1/64"
]
}
TASK [MAIN PARENT INTERFACE CONFIG] *************************************************************
ok: [rtrXXX]
TASK [SUB INTERFACES CONFIG] ********************************************************************
changed: [rtrXXX] => (item={'name': 'red', 'id': 100, 'desc': 'RED VLAN SUBINTERFACE', 'addr': '2001:678:3fc:64::XXX/64'})
changed: [rtrXXX] => (item={'name': 'purple', 'id': 101, 'desc': 'PURPLE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:65::XXX/64'})
changed: [rtrXXX] => (item={'name': 'blue', 'id': 102, 'desc': 'BLUE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:66::XXX/64'})
[WARNING]: To ensure idempotency and correct diff the input configuration lines should be
similar to how they appear if present in the running configuration on device
TASK [SHOW IPv6 INTERFACE BRIEF] ****************************************************************
ok: [rtrXXX]
TASK [ENSURE TRACE DIRECTORY EXISTS] ************************************************************
ok: [rtrXXX -> localhost]
TASK [SAVE OUTPUT] ******************************************************************************
ok: [rtrXXX]
TASK [REACHABILITY TEST] ************************************************************************
ok: [rtrXXX] => (item={'name': 'red', 'id': 100, 'desc': 'RED VLAN SUBINTERFACE', 'addr': '2001:678:3fc:64::XXX/64'})
ok: [rtrXXX] => (item={'name': 'purple', 'id': 101, 'desc': 'PURPLE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:65::XXX/64'})
ok: [rtrXXX] => (item={'name': 'blue', 'id': 102, 'desc': 'BLUE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:66::XXX/64'})
TASK [SAVE PING RESULTS] ************************************************************************
changed: [rtrXXX -> localhost]
PLAY RECAP **************************************************************************************
rtrXXX : ok=10 changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
```
All of these playbook tasks have been successfully completed. The `ok` counter has reached 10, which means that all 10 tasks have been completed.
The `changed` counter is 2, meaning 2 changes have been made. If we look for the changed keyword in the playbook run screenshot above, we can identify these configuration updates.
- IPv6 addresses have been set for the three VLANs declared in the router's `host_vars` file.
- Ping results have been saved as artifacts that prove network communications are functional.
### Step 4: Verify the configuration trace file has been created.
You can view the contents of the trace file with `cat trace/ipv6_int_brief_Router.txt`. You now have a trace of the virtual router's interface and subinterface configuration.
```bash
cat trace/ipv6_int_brief_rtrXXX.txt
```
```bash=
GigabitEthernet1 [up/up]
FE80::FAAD:CAFF:FEFE:XXX
2001:678:3FC:1C:FAAD:CAFF:FEFE:XXX
GigabitEthernet2 [up/up]
unassigned
GigabitEthernet2.100 [up/up]
FE80::FAAD:CAFF:FEFE:YYY
2001:678:3FC:64::XXX
GigabitEthernet2.101 [up/up]
FE80::FAAD:CAFF:FEFE:YYY
2001:678:3FC:65::XXX
GigabitEthernet2.102 [up/up]
FE80::FAAD:CAFF:FEFE:YYY
2001:678:3FC:66::XXX
GigabitEthernet3 [administratively down/down]
unassigned
```
## Part 4: Examining the idempotency claims of Ansible playbook tasks
And here comes the devil!
When we try to run the playbook again, we notice that the changed counter is always 2. This shouldn't be the case because the VLAN subinterfaces already have IPv6 addresses set.
Applying not-so-new addresses each time the playbook runs can cause communications to break.
```
[WARNING]: To ensure idempotency and correct diff the input configuration lines
should be similar to how they appear if present in the running configuration on device
```
When we dig deeper into the IOS configuration lines, no matter how hard we try, we always get the warning. So, the indemptency claim is broken.
### Step 1: Analyzing why idempotency is not achieved as expected
In our `router_config_playbook.yml` playbook, we chose to use the **cisco.ios.ios_config**, which sends lines of IOS XE instructions in configuration mode. In addition, the `replace: block` statement should ensure an idempotent configuration by replacing the entire specified configuration block for each sub-interface rather than attempting to merge individual lines. This should ensure that the interface configuration matches exactly what's defined in the playbook.
```yaml=
- name: SUB INTERFACES CONFIG
cisco.ios.ios_config:
lines:
- description {{ item.desc }}
- encapsulation dot1Q {{ item.id }}
- ipv6 address {{ item.addr }}
- ipv6 enable
- ipv6 nd ra suppress all
parents:
- interface {{ interface.type }}{{ interface.id }}.{{ item.id }}
match: exact
replace: block
with_items: "{{ calculated_vlans }}"
```
The problem we're encountering is symptomatic of using the syntax of a network device configuration language like IOS, which was not designed for automation in the first place.
There are two possible solutions to overcome this:
- abandon the configuration language and use only the APIs
- Break the task into multiple subtasks using elementary modules to ensure idempotency at an almost atomic level.
Since using APIs for our virtual router configuration is beyond the scope of this lab, we choose the latter.
### Step 2: Refactor the playbook to achieve indempotency
Here is a new block of 3 tasks, replacing the previous single `SUB INTERFACES CONFIG` task, each using a specific module to achieve idempotent processing.
```yaml=
- name: CONFIGURE IPv6 ADDRESSES ON SUB-INTERFACES
block:
- name: CREATE SUB-INTERFACES
cisco.ios.ios_interfaces:
config:
- name: "{{ interface.type }}{{ interface.id }}.{{ item.id }}"
description: "{{ item.desc }}"
enabled: true
state: merged
loop: "{{ calculated_vlans }}"
- name: CONFIGURE DOT1Q ENCAPSULATION AND ADDITIONAL IPv6 SETTINGS
cisco.ios.ios_config:
lines:
- encapsulation dot1Q {{ item.id }}
- ipv6 enable
- ipv6 nd ra suppress all
parents: "interface {{ interface.type }}{{ interface.id }}.{{ item.id }}"
loop: "{{ calculated_vlans }}"
- name: CONFIGURE IPv6 ADDRESSES ON SUB-INTERFACES
cisco.ios.ios_l3_interfaces:
config:
- name: "{{ interface.type }}{{ interface.id }}.{{ item.id }}"
ipv6:
- address: "{{ item.addr | ipv6 | ipaddr('address') }}/{{ item.addr | ipv6 | ipaddr('prefix') }}"
state: merged
loop: "{{ calculated_vlans }}"
rescue:
- name: Log configuration failure
ansible.builtin.debug:
msg: Failed to configure IPv6 on sub-interfaces. Check interface status and configuration.
- name: Notify on failure
ansible.builtin.fail:
msg: IPv6 interface configuration failed. See previous messages for details.
```
cisco.ios.ios_interfaces
: Manages the interface configuration on Cisco IOS devices. Define, modify, or remove physical and logical interfaces with attributes such as descriptions, MTU settings, and administrative state (enabled/disabled).
cisco.ios.ios_l3_interfaces
: Manages Layer 3 interface configurations on Cisco IOS devices, allowing for the declarative configuration of IPv4 and IPv6 addresses with appropriate subnet masks or prefixes using state-based operations (merged, replaced, overridden, or deleted).
cisco.ios.ios_config
: Pushes configuration commands to Cisco IOS devices, supporting parent-child relationships for hierarchical commands, various matching strategies (line, strict, exact), and configuration replacement methods (line, block) to manage device configurations.
As we can see, the `cisco.ios.ios_config` module is a last-resort solution when no other module in the collection provides the required configuration options.
Why use a task block?
: Using a block in this playbook allows for logical grouping of related tasks for sub-interface configuration, provides structured error handling with the rescue clause, and ensures that if any step in the configuration process fails, the playbook can gracefully report the error and take appropriate recovery actions without leaving interfaces in an inconsistent state.
### Step 3: Run the edited playbook en verify idempotency
Start by replacing the orignal `SUB INTERFACES CONFIG` task with the suggested block of three subtasks. Then run the playbook again and look at the `changed` counter value.
Here is an excerpt of the playbook run focusing on the three subinterfaces configuration processing.
```bash
TASK [CREATE SUB-INTERFACES] *****************************************************
ok: [rtrXXX] => (item={'name': 'red', 'id': 100, 'desc': 'RED VLAN SUBINTERFACE', 'addr': '2001:678:3fc:64::XXX/64'})
ok: [rtrXXX] => (item={'name': 'purple', 'id': 101, 'desc': 'PURPLE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:65::XXX/64'})
ok: [rtrXXX] => (item={'name': 'blue', 'id': 102, 'desc': 'BLUE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:66::XXX/64'})
TASK [CONFIGURE DOT1Q ENCAPSULATION AND ADDITIONAL IPv6 SETTINGS] ****************
ok: [rtrXXX] => (item={'name': 'red', 'id': 100, 'desc': 'RED VLAN SUBINTERFACE', 'addr': '2001:678:3fc:64::XXX/64'})
ok: [rtrXXX] => (item={'name': 'purple', 'id': 101, 'desc': 'PURPLE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:65::XXX/64'})
ok: [rtrXXX] => (item={'name': 'blue', 'id': 102, 'desc': 'BLUE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:66::XXX/64'})
TASK [CONFIGURE IPv6 ADDRESSES ON SUB-INTERFACES] ********************************
ok: [rtrXXX] => (item={'name': 'red', 'id': 100, 'desc': 'RED VLAN SUBINTERFACE', 'addr': '2001:678:3fc:64::XXX/64'})
ok: [rtrXXX] => (item={'name': 'purple', 'id': 101, 'desc': 'PURPLE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:65::XXX/64'})
ok: [rtrXXX] => (item={'name': 'blue', 'id': 102, 'desc': 'BLUE VLAN SUBINTERFACE', 'addr': '2001:678:3fc:66::XXX/64'})
```
We win! There is no warning message or change indicator when network interfaces have their IPv6 addresses already configured.
If we look at the playbook recap, the `changed` counter value is 1 because we saved the ping results as new artifacts.
```bash
PLAY RECAP ***********************************************************************
rtrXXX : ok=12 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
```
We can now conclude this part by acknowledging that indempotency in Ansible playbooks comes at a cost. When designing tasks, we need to think in terms of fine-grained tuning.
## Conclusion
This lab provides a practical introduction to network automation using Ansible, with a focus on both functionality and idempotency. Through hands-on exercises, you configured Ansible, backed up router configurations, and automated IPv6 addressing on router interfaces.
By creating and refining playbooks, you experienced the process of developing efficient and idempotent automation scripts. The lab highlighted the challenges of achieving true idempotency when working with network device configuration languages, and demonstrated how to overcome these challenges by breaking down tasks and using specialized Ansible modules.
You learned that while Ansible claims to provide idempotent operations, achieving this in practice often requires careful consideration and sometimes refactoring of playbook tasks. The lab showed how to analyze playbook execution, identify non-idempotent behavior, and implement solutions to ensure that repeated playbook runs produce consistent and predictable results.
This experience serves as a foundation for more advanced network automation projects, emphasizing the importance of not just automating tasks, but doing so in a way that is reliable, repeatable, and efficient. The skills acquired in this lab will be valuable as you continue to explore and implement network automation strategies in more complex environments.