New LibSSH Connection Plugin for Ansible Network Replaces Paramiko, Adds FIPS Mode Enablement

November 24, 2020 by Ganesh Nalawade

As Red Hat Ansible Automation Platform expands its footprint with a growing customer base, security continues to be an important aspect of organizations’ overall strategy. Red Hat regularly reviews and enhances the foundational codebase to follow better security practices. As part of this effort, we are introducing FIPS 140-2 readiness enablement by means of a newly developed Ansible SSH connection plugin that uses the libssh library. 

 

Ansible Network SSH Connection Basics

Since most network appliances don't support or have limited capability for the local execution of a third party software, the Ansible network modules are not copied to the remote host unlike linux hosts; instead, they run on the control node itself. Hence, Ansible network can’t use the typical Ansible SSH connection plugin that is used with linux host. Furthermore, due to this behavior, performance of the underlying SSH subsystem is critical. Not only is the new LibSSH connection plugin enabling FIPS readiness, but it was also designed to be more performant than the existing Paramiko SSH subsystem.

Screen Shot 2020-11-20 at 8.52.53 AM

The top level network_cli connection plugin, provided by the ansible.netcommon Collection (specifically ansible.netcommon.network_cli), provides an SSH based connection to the network appliance. It in turn calls the ansible.builtin.paramiko_ssh connection plugin that depends on the paramiko python library to initialize the session between control node and the remote host. After that, it creates a pseudo terminal (PTY) to send commands from the control node to the network appliance and receive the responses.

 

Why Replace Paramiko?

The primary reason to replace the paramiko library is that it doesn’t guarantee FIPS readiness and thus limits the Ansible network capability to run in environments that mandate FIPS mode to be enabled. Paramiko also isn’t the speediest of connection plugins, so that can also be enhanced. Therefore, the new ansible.netcommon.libssh connection plugin can now be easily swapped in for paramiko. The ansible.netcommon Collection now contains this by default, and can be used for testing purposes until the codebase becomes more stable (it is currently Technology Preview).

Comparing the connection flow to the above, the top level network_cli connection plugin that is provided by the ansible.netcommon Collection (specifically ansible.netcommon.network_cli) still provides an SSH based connection to the network appliance. It in turn calls the ansible.netcommon.libssh connection plugin that depends on the ansible-pylibssh python library to initialize the session between control node and the remote host. This python library is essentially a cython wrapper on top of the libssh C library. It then creates pseudo terminals (PTY) over SSH using python.

 

Switching Ansible Playbooks to use LibSSH

With the ansible.netcommon Collection version 1.0.0, a new configuration parameter within ansible.netcommon.network_cli connection plugin was added, which allows for ssh_type be set to either libssh or paramiko. 

If the value of the configuration parameter is set to libssh, it will use the ansible.netcommon.libssh connection plugin, which in turn uses the ansible-pylibssh python library that supports FIPS readiness. If the value is set to paramiko, it will continue to use the default ansible.builtin.paramiko connection plugin that relies on the paramiko python library. 

Again, the default value is set to paramiko, but in the future plans are to change the default to libssh.

 

Installing and Configuring LibSSH

In order to utilize the LibSSH plugin, you must first install the ansible-pylibssh python library from PyPI via the following command:

pip install ansible-pylibssh

NOTES:

  • The current PyPI installation method bundles the correct version of LibSSH library and its dependencies as platform-specific wheels that don’t rely on any OS-level libraries in runtime.
  • Future plans include creation, publishing, and maintenance of stand-alone RPM and DEB packages for the ansible-pylibssh library that can be installed with well-known Linux package managers. These will install the required system libssh version and its dependencies on the control node. FYI, Red Hat Enterprise Linux 8.1 and later contains the proper libssh package version and its dependencies.
  • The current primary use case for using LibSSH with Ansible is for connecting to network devices. Connecting to other types of endpoints (such as Linux) will be officially enabled at a later date.

 

Using LibSSH in Ansible Playbooks

Method 1:  The ssh_type configuration parameter can be set to use libssh in the active ansible.cfg file of your project as shown below:

[persistent_connection]
ssh_type = libssh

Method 2:  Set the ANSIBLE_NETWORK_CLI_SSH_TYPE environment variable as shown below:

$export ANSIBLE_NETWORK_CLI_SSH_TYPE=libssh

Method 3:  Set the ansible_network_cli_ssh_type parameter to libssh within your playbook at the play level (as shown in below example).

NOTE: This setting can be made at the individual task level, but only if the connection to the remote network device is not already established. That is, if the first task uses paramiko, then all subsequent tasks in the play must use paramiko even if libssh is specified in any subsequent tasks.

 

Troubleshooting LibSSH Connections

To quickly verify the libssh transport is set correctly, you can run the below playbook using the ansible-playbook command line with verbose flag (-vvvv) added. Before running, ensure the inventory file is set correctly.

This example playbook uses the cisco.ios Collection and must first be installed from Ansible Galaxy or Ansible Automation Platform on your Ansible control node.

- hosts: "changeme"
  gather_facts: no
  connection: ansible.netcommon.network_cli
  vars:
    ansible_network_os: cisco.ios.ios
    ansible_user: "changeme"
    ansible_password: "changeme"
    ansible_network_cli_ssh_type: libssh
  tasks:
  - name: run show version command
    ansible.netcommon.cli_command:
      command: show version

  - name: run show interface command
    ansible.netcommon.cli_command:
       command: show interfaces

https://gist.github.com/ganeshrn/78149adca85c809b69ed1b5f5262844c

In the output verbose logs, you should see the line “ssh type is set to libssh” displayed on the console, which confirms the configuration is set correctly.

 

Next Steps and Resources

  • Start testing your Ansible network playbooks by setting the configuration to use the ansible-pylibssh library.
  • Help with performance profiling of your existing playbook of  ansible-pylibssh library with respect to paramiko library.
  • Get involved with the ansible-pylibssh project (https://github.com/ansible/pylibssh)
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Topics:
Network Automation


 

Ganesh Nalawade

Extensive experience in software design and development, currently working for Red Hat as Principal Software Engineer in Ansible Network Engineering.


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