SSH CLI commands

Preparing commands and templates

CLI commands are implemented in the Connector() class by using the Netmiko library. This provides standard SSH access into a device.

Predefined CLI commands are run by calling Connector().run_command(), whereas form template input commands are calling Connector().run_command_string(). See switches/connect/connector.py, around line 1210

These functions expand the commands and templates to regular strings to send over SSH.

Executing commands

Both functions then call Connector()._execute_command() to execute the SSH command. See switches/connect/connector.py, around line 1160

This function calls self.netmiko_connect() to create a vendor-specific netmiko.ConnectHandler. The ConnectHandler() is Netmiko’s SSH object. It then uses that handle to send and receive data over SSH via calls to netmiko.send_command_timing() or netmiko.send_command()

Implementing CLI functionality

Drivers can override the self.execute_command() functionality to implement their own mechanism to execute CLI commands on a device.

An example if this is the Arista eAPI driver, in switches/connect/arista_eapi/connector.py, the _execute_command() function. This uses the eAPI in “text” mode to run a command. Note: for this device type, this is significanly faster then the normal SSH implementation via Netmiko.

Additionally, the Aruba AOS-S driver implements _execute_command() to implement using their REST API, instead of SSH.

Note: it is possible to implement a complete SSH interface to manage devices. The Napalm library attempts to do this, but lacks support for 802.1q, PoE, and more. This exercise is left to the reader…