Ansible Juniper Networking

Ansible and Juniper Junos – Using SSH Keys

Previous posts introduced basics connection methods to manage Juniper devices using Ansible playbooks. The inventory files had sensitive information and credentials which should not be accessible to anyone.

SSH and NETCONF over SSH requires client authentication, for example with and username and password, which could looks like this:

admin> show configuration system login 
user admin {
    uid 2000;
    class super-user;
    authentication {
        encrypted-password "$1$./TeE4CZ$uAMigDedlRuuJgcZx4hYk0"; ## SECRET-DATA

If you are a frequent SSH user, maybe you are aware that there are other login methods besides using usernames and passwords. By using a key-pair, with public and private keys, a password is no longer needed. The public key is installed on the remote host, and the private key is kept on the control node.

Although by using keys a password is no longer needed, a passphrase can be used with a key, adding an additional security factor to the connection. In fact, using SSH keys with passphrases is considered best practice. However, a private key with a passphrase is less useful for scheduled automation tasks because an operator may not be available to enter the passphrase at the scheduled time.

Creating a Key Pair

A key pair is a set of two cryptographic keys, a public one and a private one. The public key, as its name says, is the one we expose to the public. The private key, must be kept in a secure location.

To create a key pair, lauch ssh-keygen on a new console and follow the prompts. This utility will create two files, which are the public and private keys. Use the -f flag to specify the destination of the output files.

arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ ssh-keygen -f ./juniper-hosts.key
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in ./juniper-hosts.key.
Your public key has been saved in ./
The key fingerprint is:
SHA256:Kc/MZ11dLlXpcrK9PKO4L6XzaTrdczaek1ydzaFTFXw arturo@arturo-ThinkPad-L440
The key's randomart image is:
+---[RSA 2048]----+
|              ..+|
|               oE|
|              . =|
|         .   o O.|
|      . S     @.B|
|       *   . * +=|
|        = o = = +|
|         o =.o.%+|
|           +X=o+B|
arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ ls 

Now that we have created the key pair, let’s examine them to find out how a key looks like.

This is the private key, which in fact is a plain text file with a RSA key inside it.

arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ cat juniper-hosts.key

And the public keys looks like this.

arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ cat 
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCfRe11M8nFYdAd5aLwjBI4a2yBbBbfPzpn3V50fR0FLpJYPOax5ayFJMPY90PwRTSYZpzVX36tYglgjDRVmWlN4QqI2dL7X994fGWf5LQsvCf3UTp+BVG3qQT/25O/bXs9rl4/kcts+5LA+xUzBGB0IkvWlggVqAkvKuxqQNYTSoO0FdnR96d2ZSvo2usIuh+McGREBK+In0ThW/Hhiqsb1qT7aNfbWDQtE3Fn+cW/a4fBV4iCJsL7UmJn8gZoFI0Ki8XXfXBvUBTIublnkM28zqG7YLr5wxM01Dl+IF+AymvJuhbj4xUIYlDfUS2HIUTHRc+COiz8RxL0+njfo6mn arturo@arturo-ThinkPad-L440

This keypair can authenticate an user which connects via SSH.

Installing the public key on Junos

We already know that a basic authentication schema on Junos looks like this.

admin> show configuration system login 
user admin {
    uid 2000;
    class super-user;
    authentication {
        encrypted-password "$1$kYNQ.bg0$4T3W7GAPuXwsX3nbbsRCb/"; ## SECRET-DATA

The main idea of using SSH keys, is to avoid user interaction, by trusting the keys instead of a credentials combination.

As seen above, the keys are plain text files. We need to install the public key on the Junos configuration, either configuring it manually, or using Ansible to configure it.

Manually configuring the key

I added a new user called ansible, set its class as super-user and configured its authentication as ssh-rsa.

admin# show system login | display set                                                                                                                                 
set system login user admin uid 2000
set system login user admin class super-user
set system login user admin authentication encrypted-password "$1$MExZQJdK$lLhnzSw.CLSMQg5bdIiws."
set system login user ansible uid 2001
set system login user ansible class super-user
set system login user ansible authentication ssh-rsa "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCfRe11M8nFYdAd5aLwjBI4a2yBbBbfPzpn3V50fR0FLpJYPOax5ayFJMPY90PwRTSYZpzVX36tYglgjDRVmWlN4QqI2dL7X994fGWf5LQsvCf3UTp+BVG3qQT/25O/bXs9rl4/kcts+5LA+xUzBGB0IkvWlggVqAkvKuxqQNYTSoO0FdnR96d2ZSvo2usIuh+McGREBK+In0ThW/Hhiqsb1qT7aNfbWDQtE3Fn+cW/a4fBV4iCJsL7UmJn8gZoFI0Ki8XXfXBvUBTIublnkM28zqG7YLr5wxM01Dl+IF+AymvJuhbj4xUIYlDfUS2HIUTHRc+COiz8RxL0+njfo6mn arturo@arturo-ThinkPad-L440"

The SSH public key is copied and pasted between double quotes.

Using Ansible to configure the key

Altough the key can be configured manually on the remote hosts, what if we have hundreds, or thousands of hosts to configure?

The idea behind this series of posts is to use Ansible whenever possible, so, let’s write a quick playbook to automate the key configuration.

rturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ cat junos-install-ssh-key.yaml 
- hosts: all
  gather_facts: no

    - auth_key: "{{lookup('file', '{{ key_file }}')}}"    

    - name: Install SSH key on remote host
          - set system login user ansible authentication ssh-rsa "{{ auth_key }}"
          - set system login user ansible class super-user

The playbook starts as usual, matching all hosts in the inventory, and without gathering facts, just for the sake of speed.

On vars, we are using the lookup plugin to read from a file and store its contents on a variable. Lookup can retrieve data from multiple sources, for example, take a secret from Hashicorp’s Vault. In this scenario, it will read a file which name is take from the key_file variable from the inventory.

It is possible to set a fixed file name on the playbook, but by taking the filename as a variable from the inventory, it gives us more flexibility. We could have multiple keys and rotate them by just changing the file name on the inventory, or use different keys per host group, and still apply the playbook to the full inventory, while using the proper key for each group.

The inventory for this playbook looks like the following. Notice the key_file variable which tells the playbook where to look for the key.

arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ cat junos-hosts.yaml 
      ansible_connection: netconf
      ansible_network_os: junos
      ansible_user: admin
      ansible_password: Password$1

Running the playbook to install the key

The current configuration of router logins is:

admin> show configuration system login 
user admin {
    uid 2000;
    class super-user;
    authentication {
        encrypted-password "$1$MExZQJdK$lLhnzSw.CLSMQg5bdIiws."; ## SECRET-DATA

Let’s run the playbook to apply the new configuration which will create the ansible user, set ssh-rsa authentication for it, and set its class as super-user.

arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ ansible-playbook junos-install-ssh-key.yaml -i junos-hosts.yaml 

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

TASK [Install SSH key on remote host] **************************************************
changed: []

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

Ok, the playbook executed with no errors, and Ansible says there is 1 changed host, which is what we expected.

Let’s check the router configuration again.

admin> show configuration system login    
user admin {
    uid 2000;
    class super-user;
    authentication {
        encrypted-password "$1$MExZQJdK$lLhnzSw.CLSMQg5bdIiws."; ## SECRET-DATA
user ansible {
    uid 2001;
    class super-user;
    authentication {
        ssh-rsa "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCfRe11M8nFYdAd5aLwjBI4a2yBbBbfPzpn3V50fR0FLpJYPOax5ayFJMPY90PwRTSYZpzVX36tYglgjDRVmWlN4QqI2dL7X994fGWf5LQsvCf3UTp+BVG3qQT/25O/bXs9rl4/kcts+5LA+xUzBGB0IkvWlggVqAkvKuxqQNYTSoO0FdnR96d2ZSvo2usIuh+McGREBK+In0ThW/Hhiqsb1qT7aNfbWDQtE3Fn+cW/a4fBV4iCJsL7UmJn8gZoFI0Ki8XXfXBvUBTIublnkM28zqG7YLr5wxM01Dl+IF+AymvJuhbj4xUIYlDfUS2HIUTHRc+COiz8RxL0+njfo6mn arturo@arturo-ThinkPad-L440"; ## SECRET-DATA

There is a new user called ansible, with all the parameters we specified. That’s great!

Authenticating using keys

I wrote another playbook to show the system uptime

- hosts: all
  gather_facts: no

    - name: Get uptime
            - show system uptime
      register: uptime
    - name: Show uptime
      debug: var=uptime

And our inventory now looks like this.

      ansible_connection: netconf
      ansible_network_os: junos
      ansible_user: ansible
      ansible_ssh_private_key_file: juniper-hosts.key
      ansible_python_interpreter: auto_silent

There is no plain text password, but instead, by setting up the ansible_ssh_private_key_file variable, we are instructing Ansible to authenticate using the private key.

arturo@arturo-ThinkPad-L440:~/Desktop/ansible-01$ ansible-playbook junos-auth-with-key.yaml -i junos-hosts-w-key.yaml 

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

TASK [Get uptime] **********************************************************************
ok: []

TASK [Show uptime] *********************************************************************
ok: [] => {
    "uptime": {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/bin/python"
        "changed": false, 
        "failed": false, 
        "stdout": [
            "Current time: 2020-01-12 16:25:10 UTC\nSystem booted: 2020-01-12 13:42:06 UTC (02:43:04 ago)\nProtocols started: 2020-01-12 13:42:27 UTC (02:42:43 ago)\nLast configured: 2020-01-12 16:09:02 UTC (00:16:08 ago) by admin\n 4:25PM  up 2:43, 3 users, load averages: 0.08, 0.02, 0.01"
        "stdout_lines": [
                "Current time: 2020-01-12 16:25:10 UTC", 
                "System booted: 2020-01-12 13:42:06 UTC (02:43:04 ago)", 
                "Protocols started: 2020-01-12 13:42:27 UTC (02:42:43 ago)", 
                "Last configured: 2020-01-12 16:09:02 UTC (00:16:08 ago) by admin", 
                " 4:25PM  up 2:43, 3 users, load averages: 0.08, 0.02, 0.01"

PLAY RECAP *****************************************************************************            : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 

This is great, now Ansible authenticates using the SSH key. You maybe are thinking:

“Do i have to edit my inventory every time i want to use keys?”

The answer is, no, and in the next post we will set a interactive prompt to connect using user and password to run the first playbook, which will configure the key, and then we will run all the other playbooks connecting with this key.

Stay tuned for more!

By Arturo

Always computing, connecting people and machines.

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