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This blog is going to go over the concepts of using Ansible to interact with a private network through a bastion host. The use of bastion hosts is not new to the industry—they have been used for a while by many companies that need to give users access to private networks. Bastion hosts are typically public facing, hardened systems that work as an entrypoint to systems that are behind a firewall or any other restricted locations.
Set up SSH public key authentication with bastion host
When interacting with a bastion host, the recommended first step is to set up SSH public keys and authenticate with the bastion host.
If an SSH key doe not already exist, create it by issuing the command ssh-keygen -t rsa
root@eb54369adc49:/ntc# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:T5YDoF91QrJk2ZN1b7OYq9Pfn3OWVW518iCJHGIQKeQ root@eb54369adc49
The key's randomart image is:
+---[RSA 2048]----+
| .. +++++oo . |
| ....+++=o . . |
| E. .+o + . .o|
| . . .o.o =.*|
| . S = + *+|
| + . . =|
| . .. .o|
| ... o=|
| .. .+*|
+----[SHA256]-----+
root@eb54369adc49:/ntc#
root@eb54369adc49:/ntc#
Since this is just for demonstration, I’ve kept everything as default when creating the keys.
Note: Click here if you want to know more about how to set up an SSH public key with more details.
After creating the public key, the ssh-copy-id Linux command can be used to transfer the id_rsa.pub public key to the bastion host.
root@eb54369adc49:/ntc#
root@eb54369adc49:/ntc# ssh-copy-id ntc@bastion
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
ntc@bastion password:
Number of key(s) added: 1
Now try logging into the machine, with: "ssh 'ntc@bastion'"
and check to make sure that only the key(s) you wanted were added.
root@eb54369adc49:/ntc#
Finally, attempt to SSH into the bastion host and make sure it works as expected. The workstation should log in through SSH without having to provide a password.
root@eb54369adc49:/ntc# ssh ntc@bastion
Welcome to Ubuntu 16.04.1 LTS (GNU/Linux 4.4.0-59-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
466 packages can be updated.
321 updates are security updates.
New release '18.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Mon Jan 13 13:44:58 2020 from 71.52.24.123
ntc@bastion:~$
ntc@bastion:~$ exit
logout
Connection to bastion closed.
root@eb54369adc49:/ntc#
There are many different ways of creating a public key and transferring it to the remote host. This transfer can also be handled via Ansible, as the below playbook shows:
---
- name: Generate Key
hosts: localhost
connection: local
gather_facts: no
tasks:
- name: Generate an OpenSSH keypair with the default values (4096 bits, rsa)
openssh_keypair:
path: /root/.ssh/id_rsa
owner: root
group: root
- name: Deploy public key to remote host
shell: ssh-copy-id ntc@bastion
Setting up Ansible to Interact with a Cisco IOS Device through a Bastion Host
Now that it is possible to authenticate into the bastion host only using SSH keys and not require user/passwords, it’s time to build the Ansible inventory file with the devices that are going to be targeted by Ansible. Before creating the inventory file, notice how the only way to interact with the Cisco csr1 device is through the bastion host.
# Topology
┏━━━━━━━━━━━━━━┓ ┏━━━━━━━━━━━━━━┓ ┏━━━━━━━━━━━━┓
┃ Container ┃──────────┃ Bastion host ┃──────────┃ csr1 ┃
┗━━━━━━━━━━━━━━┛ ┗━━━━━━━━━━━━━━┛ ┗━━━━━━━━━━━━┛
This first test is using the ping command to ping the csr1 device from the local container. The results should come back with 100% packet loss.
root@eb54369adc49:/ntc#
root@eb54369adc49:/ntc#
root@eb54369adc49:/ntc# ping csr1 -c 5
PING csr1 (54.84.81.49) 56(84) bytes of data.
--- csr1 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4176ms
After using the SSH command to access the bastion host, the ping command is used again to show that there is IP connectivity between the bastion host and the networking device.
root@eb54369adc49:/ntc#
root@eb54369adc49:/ntc# ssh ntc@bastion
Welcome to Ubuntu 16.04.1 LTS (GNU/Linux 4.4.0-59-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
466 packages can be updated.
321 updates are security updates.
New release '18.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Mon Jan 13 14:38:26 2020 from 71.52.24.123
ntc@bastion:~$
ntc@bastion:~$ ping csr1 -c 5
PING csr1 (10.0.0.51) 56(84) bytes of data.
64 bytes from csr1 (10.0.0.51): icmp_seq=2 ttl=255 time=2.34 ms
64 bytes from csr1 (10.0.0.51): icmp_seq=3 ttl=255 time=2.26 ms
64 bytes from csr1 (10.0.0.51): icmp_seq=4 ttl=255 time=1.99 ms
64 bytes from csr1 (10.0.0.51): icmp_seq=5 ttl=255 time=2.23 ms
--- csr1 ping statistics ---
5 packets transmitted, 4 received, 20% packet loss, time 4013ms
rtt min/avg/max/mdev = 1.994/2.209/2.342/0.138 ms
ntc@bastion:~$
Now that you can verify direct connectivity from the container to the csr1 device is only possible through the bastion host, the ProxyCommand can be used to gain access to the Cisco device from the container.
Note: ProxyCommand is an SSH builtin command feature to provide support for proxy use cases.
root@eb54369adc49:/ntc#
root@eb54369adc49:/ntc# ssh -o ProxyCommand="ssh -W %h:%p ntc@bastion" ntc@csr1
The authenticity of host 'csr1 (<no hostip for proxy command>)' can't be established.
RSA key fingerprint is SHA256:BaRERnJrQ4vzALKQELc6lIs7Kujbe3UCPffPcAhcRKg.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'csr1' (RSA) to the list of known hosts.
Password:
csr1#
csr1#
Playbook
For this test the ios_command and ios_config will be used. The backup parameter has been enabled to show that the backup files are stored in the local machine and not on the bastion host.
---
- name: Cisco IOS Playbook
hosts: ios
connection: network_cli
gather_facts: no
tasks:
- name: SHOW VERSION
ios_command:
commands: show version
- name: CONFIGURE SNMP COMMUNITY
ios_config:
commands: snmp-server community ntc-blog RW
backup: true
Inventory
For now, only the basic credentials and device type are required to target the device.
[all:vars]
ansible_user=ntc
ansible_ssh_password=ntc123
[ios]
csr1
[ios:vars]
ansible_network_os=ios
Note: There is a dedicated group vars for IOS only for now, since a Juniper device will be tested later in this blog too.
First Execution of Playbook
Similar to the previous tests, the local machine should not be able to communicate with the Cisco device, since it does not have direct access to the private network.
root@eb54369adc49:ntc$ ansible-playbook -i inventory bastion_playbook.yml
PLAY [Cisco IOS Playbook] ******************************************************************
TASK [SHOW VERSION] ************************************************************************
fatal: [csr1]: FAILED! => {"changed": false, "msg": "timed out"}
PLAY RECAP *********************************************************************************
csr1 : ok=0 changed=0 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0
root@eb54369adc49:ntc$
Executing a Playbook against a Cisco IOS Device through a Bastion Host
To be able to communicate with the Cisco device the ProxyCommand needs to be executed when trying to SSH into the device. To start using the ProxyCommand with Ansible the ansible_ssh_common_args, a variable needs to be added to the inventory file.
[all:vars]
ansible_user=ntc
ansible_ssh_password=ntc123
[ios]
csr1
[ios:vars]
ansible_network_os=ios
ansible_ssh_common_args=ProxyCommand="ssh -W %h:%p ntc@bastion"
More details can be found in the Ansible documentation about how to use the ansible_ssh_common_args and ProxyCommand. For now, I’ve added a device to the inventory file with the needed credentials, and the ProxyCommand used earlier and tested through the Linux terminal.
The Ansible playbook can now be executed normally using the standard ansible-playbook command. The only modification needed to interact with the networking device was enabling SSH keys and using the ansible_ssh_common_args in the inventory file.
root@eb54369adc49:/ntc# ansible-playbook -i inventory bastion_playbook.yml -v
Using /ntc/ansible.cfg as config file
PLAY [Cisco IOS Playbook] ***********************************************************
TASK [SHOW VERSION] ***************************************************************
ok: [csr1] => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}
"changed": false, "stdout": ["Cisco IOS XE Software,
Version 16.06.02\nCisco IOS Software [Everest], Virtual XE Software
(X86_64_LINUX_IOSD-UNIVERSALK9-M), Version 16.6.2, RELEASE
SOFTWARE (fc2)\nTechnical Support: http://www.cisco.com
techsupport\nCopyright (c) 1986-2017 by Cisco Systems, Inc
\nCompiled Wed 01-Nov-17 07:24 by mcpre\n\n\nCisco IOS-X
software, Copyright (c) 2005-2017 by cisco Systems, Inc
\nAll rights reserved. Certain components of Cisco IOS-XE
software are\nlicensed under the GNU General Public License" ...omitted]]}
TASK [CONFIGURE SNMP COMMUNITY] ***********************************************************
changed: [csr1] => {"backup_path": "/ntc/backup/csr1_config.2020-01-13@22:02:16", "banners":
{}, "changed": true, "commands": ["snmp-server community ntc-blog RW"],
"date": "2020-01-13", "filename": "csr1_config.2020-01-13@22:02:16", "shortname": "/ntc
backup/csr1_config", "time": "22:02:16", "updates": ["snmp-server community ntc-blog RW"]}
PLAY RECAP *********************************************************************************
csr1 : ok=2 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
Setting up Ansible to Interact with a Juniper vMX Device using NETCONF through a Bastion Host
To interact with a Juniper device via a bastion host that uses NETCONF, a different variable is required and a configuration file needs to be built. This link gives some details on different ways to enable the feature, but for this test I’ll be adding the ansible_netconf_ssh_config=./ntc/netconf_proxy_config.cfg variable with the path to my netconf_proxy_config.cfg file.
Note: Even thought the Ansible documentation is not entirely clear why
ansible_ssh_common_argsdoes not work with NETCONF devices, maybe this link can provide insight to that question.
[all:vars]
ansible_user=ntc
ansible_ssh_password=ntc123
[ios]
csr1
[ios:vars]
ansible_network_os=ios
ansible_ssh_common_args=ProxyCommand="ssh -W %h:%p ntc@bastion"
[vmx]
vmx1
[vmx:vars]
ansible_network_os=junos
ansible_netconf_ssh_config=./ntc/netconf_proxy_config.cfg
Setting up the netconf_proxy_config.cfg and ansible.cfg file
The Ansible documentation shows how to build a proper netconf_proxy_config.cfg file. However, since I’m only testing with a single device, the only requirement is the ProxyCommand that will establish the SSH connection with the bastion host and the Juniper device.
ProxyCommand ssh -W %h:%p ntc@bastion
The next step will be to add a second play using the correct modules to interact with a Juniper device.
Executing a Playbook against a Juniper vMX Device using NETCONF through a Bastion Host
The example playbook has been extended to include not only the original Cisco IOS tasks, but an additional play to run the equivalent on Juniper devices. The goal is to run a show version and make a configuration change to add an SNMP community to the device configuration.
---
- name: Cisco IOS Playbook
hosts: ios
connection: network_cli
gather_facts: no
tags: cisco
tasks:
- name: SHOW VERSION
ios_command:
commands: show version
- name: CONFIGURE SNMP COMMUNITY
ios_config:
commands: snmp-server community ntc-blog RW
backup: true
- name: Juniper vMX Playbook
hosts: vmx
connection: netconf
gather_facts: no
tags: juniper
tasks:
- name: SHOW VERSION
junos_command:
commands: show version
- name: CONFIGURE SNMP COMMUNITY
junos_config:
commands: set snmp community ntc-blog authorization read-write
After building the playbook, it’s time to execute it and see the results. In this case I ran the playbook and added a tag so only the Juniper play gets executed.
root@eb54369adc49:/ntc# ansible-playbook -i inventory bastion_playbook.yml --tags juniper -v
Using /ntc/ansible.cfg as config file
PLAY [Cisco IOS Playbook] *******************************************************************
PLAY [Juniper IOS Playbook] *****************************************************************
TASK [SHOW VERSION] *************************************************************************
ok: [vmx1] => {"changed": false, "stdout": ["Hostname: vmx1\nModel: vmx\nJunos: 15.1F4.15
\nJUNOS Base OS boot [15.1F4.15]\nJUNOS Base OS Software Suite [15.1F4.15]\nJUNOS Crypto
Software Suite [15.1F4.15]\nJUNOS OnlineDocumentation [15.1F4.15]\nJUNOS 64-bit Kernel Software
Suite [15.1F4.15]\nJUNOS Routing Software Suite [15.1F4.15]\nJUNOS Runtime Software Suite [15.1F4. 15]
\nJUNOS 64-bit Runtime Software Suite [15.1F4.15] \nJUNOS Services AACL PIC package [15.1F4.15] \nJUNOS
Services Application Level Gateway (xlp64) [15.1F4.15]\nJUNOS Services ..omitted"]]}
TASK [CONFIGURE SNMP COMMUNITY] *************************************************************
changed: [vmx1] => {"changed": true}
PLAY RECAP **********************************************************************************
vmx1 : ok=2 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
Conclusion
In order to use Ansible through a bastion host with core modules, SSH keys are recommended. When interacting with devices that support NETCONF, the ansible_netconf_ssh_config variable is required to be enabled and for traditional SSH devices the ansible_ssh_common_args is required.
Other third party modules like ntc_show_command or NAPALM can also be used but will not be able to support ansible_ssh_common_args or ansible_netconf_ssh_config. In this case, the delegate_to argument will be needed to use a third party module with a jump-host/bastion-host.
-Hector
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