Package ncdiff is a simplified version of yang.ncdiff. Both were initially developed internally in Cisco and is now available to the general public through open-source. yang.ncdiff is integrated into the modular architecture of pyATS framework, while ncdiff is more lightweight and standalone.

Docs: https://ncdiff.readthedocs.io/en/latest/

GitHub: https://github.com/CiscoTestAutomation/ncdiff/

Configuration is a major goal of NetConf. RFC 6241 claims "NETCONF defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices."

Each YANG model tries to abstract one aspect of configuration by a hierarchical schema. There might be a model to describe OSPF configuration, and another model to describe BGP configuration, etc.

For one model, there are many different possible configurations. Each configuration might be considered as a state, and it can be obtained by a get-config request. Between two states, there are two directional transitions: from state A to state B, and from state B to state A. Each transition corresponds to an edit-config RPC.

Primarily, there are three classes defined in this module: ModelDevice, Config and ConfigDelta.

• A modeled device supporting multiple models - ModelDevice
• A config state of multiple models - Config
• A config delta between two configs - ConfigDelta

Quick examples can be found in section Tutorial.

• Connect to a Netconf device by an instance of ModelDevice
• Download, compile and print model schemas
• Get config states
• Calculate diff of two instances of Config, so edit-config can be sent to the device to toggle between config state A and B
• Given a config state and an edit-config, calculate the new config state
• Support XPATH on Config and RPCReply
• Instantiate Config objects by Netconf rpc-reply
• Present ConfigDelta objects in the form of Netconf (a config content of edit-config).

Summary of config operations:

=============   =========   =============   =========   =============   ==============================
operand         operator    operand         equality    result          note
=============   =========   =============   =========   =============   ==============================
Config          \+          Config          =           Config          Combine two config
Config          \+          ConfigDelta     =           Config          Apply edit-config to a config
ConfigDelta     \+          ConfigDelta     =           N/A             Not implemented
ConfigDelta     \+          Config          =           Config          Apply edit-config to a config
Config          \-          Config          =           ConfigDelta     Generate an edit-config
Config          \-          ConfigDelta     =           Config          Apply an opposite edit-config
ConfigDelta     \-          ConfigDelta     =           N/A             Not implemented
ConfigDelta     \-          Config          =           N/A             Not implemented
=============   =========   =============   =========   =============   ==============================

ncdiff module requires a few packages. Some of them are required implicitly:

• lxml http://lxml.de/index.html (required by ncclient)
• paramiko https://pypi.org/project/paramiko/ (required by ncclient)

Others are required directly:

• ncclient http://ncclient.readthedocs.io/en/latest/
• pyang https://pypi.org/project/pyang/

Installation of these packages are normally smooth. Based on our support experience, most issues are related to lxml and paramiko installation.

This package can be installed from pypi server.

First-time installation steps:

    pip install ncdiff

Steps to upgrade to latest:

    pip install --upgrade ncdiff