Chapter 2: Connecting to Network Devices via SSH Using Paramiko

When administrating IT devices from a remote location, be it network equipment or servers, SSH has become the standard. With its secure transport and various authentication methods, it's a safe choice that is widely used to this day to administer and configure servers or network devices. It is thus only natural when getting started with programmability and network automation, to find a way of issuing SSH commands not by hand but from a script. With this, you can take a sequence of commands you used to type into the device by hand and execute them programmatically on one or more devices. The last part is crucial. With a script that executes commands for you, you can easily apply the same sequence of commands to another device.

While we could implement the SSH protocol ourselves, this would be cumbersome work. Luckily, the Python community has already developed an SSH client library that is available for our use, called Paramiko.

In this chapter, we are going to learn the basics of programmatically connecting to a network device using SSH. We are going to use Cisco devices for our examples but the workflow is the same regardless of the vendor.

In this chapter, we will work through the following recipes:

• Initiating an SSH session with Paramiko
• Executing a command via SSH
• Reading the output of an executed command
• Executing the same command against multiple devices
• Executing a sequence of commands
• Using public/private keys for authentication
• Loading local SSH configuration