Programmability Configuration Guide for Cisco NCS 4000 Series Routers, IOS XR Release 6.5.x
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Drive Network Automation Using Programmable YANG Data Models
Table 1. Feature History
Feature Name
Release Information
Feature Description
NCS 4000 YANG Data models
Cisco IOS XR Release 6.5.31
YANG data models are supported on NCS 4000 instead of CLI commands.
The data models are written in an industry-defined language and is used
to automate configuration tasks and retrieve operational data across
heterogeneous devices in a network. Using model-driven programmability
results in scalability.
Typically, a network operation center is a heterogeneous mix of various devices at
multiple layers of the network. Such network centers require bulk automated
configurations to be accomplished seamlessly. CLIs are widely used for configuring and
extracting the operational details of a router. But the general mechanism of CLI
scraping is not flexible and optimal. Small changes in the configuration require
rewriting scripts multiple times. Bulk configuration changes through CLIs are cumbersome
and error-prone. These limitations restrict automation and scale. To overcome these
limitations, you need an automated mechanism to manage your network.
Cisco IOS XR supports a programmatic way of configuring and collecting operational data
of a network device using data models. They replace the process of manual configuration,
which is proprietary, and highly text-based. The data models are written in an
industry-defined language and is used to automate configuration task and retreive
operational data across heterogeneous devices in a network. Although configurations
using CLIs are easier and human-readable, automating the configuration using
model-driven programmability results in scalability.
Model-driven programmability provides a simple, flexible and rich framework for device
programmability. This programmability framework provides multiple choices to interface
with an IOS XR device in terms of transport, protocol and encoding. These choices are
decoupled from the models for greater flexibility.
The following image shows the layers in model-driven programmability:
Figure 1. Model-driven Programmability Layers
Data models provides access to the capabilities of the devices in a network using Network
Configuration Protocol. The operations on the router are carried out by the protocols
using YANG models to automate and programme operations in a network.
Benefits of Data Models
Configuring routers using data models overcomes drawbacks posed by traditional
router management because the data models:
Provide a common model for configuration and operational state data, and
perform NETCONF actions.
Use protocols to communicate with the routers to get, manipulate and
delete configurations in a network.
Automate configuration and operation of multiple routers across the
network.
This article describes how you benefit from using data models to programmatically
manage your network operations.
YANG Data Model
A YANG module defines a data model through the data of the router, and the hierarchical
organization and constraints on that data. Each module is uniquely identified by a
namespace URL. The YANG models describe the configuration and operational data, perform
actions, remote procedure calls, and notifications for network devices.
The YANG models must be obtained from the router. The models define a valid structure
for the data that is exchanged between the router and the client. The models are used by
NETCONF enabled applications.
YANG models can be:
Cisco-specific models: For a list of supported models and their
representation.
For more details about YANG, refer RFC 6020 and 6087.
Components of a YANG Module
A YANG module defines a single data model. However, a module can reference
definitions in other modules and sub-modules by using one of these statements:
import imports external modules
include includes one or more sub-modules
augment provides augmentations to another module, and defines the
placement of new nodes in the data model hierarchy
when defines conditions under which new nodes are valid
prefix references definitions in an imported module
The YANG models configure a feature, retrieve the operational state of the router,
and perform actions.
Note
The JSON data is based on YANG module name and not YANG
namespace.
Structure of YANG Data Model
Data models handle the following types of requirements on routers (RFC 6244):
Configuration data: A set of writable data that is required to
transform a system from an initial default state into its current state. For
example, configuring entries of the IP routing tables, configuring the
interface MTU to use a specific value, configuring an ethernet interface to
run at a given speed, and so on.
Operational state data: A set of data that is obtained by the system
at runtime and influences the behavior of the system in a manner similar to
configuration data. However, in contrast to configuration data, operational
state data is transient. The data is modified by interactions with internal
components or other systems using specialized protocols. For example,
entries obtained from routing protocols such as OSPF, attributes of the
network interfaces, and so on.
Actions: A set of NETCONF actions that support robust network-wide
configuration transactions. When a change is attempted that affects multiple
devices, the NETCONF actions simplify the management of failure scenarios,
resulting in the ability to have transactions that will dependably succeed
or fail atomically.
For more information about Data Models, see RFC 6244.
YANG data models can be represented in a hierarchical, tree-based structure with
nodes. This representation makes the models easy to understand.
Each feature has a defined YANG model, which is synthesized from schemas. A model in
a tree format includes:
Top level nodes and their subtrees
Subtrees that augment nodes in other YANG models
Custom RPCs
YANG defines four node types. Each node has a name. Depending on the node type, the
node either defines a value or contains a set of child nodes. The nodes types for
data modeling are:
leaf node - contains a single value of a specific type
leaf-list node - contains a sequence of leaf nodes
list node - contains a sequence of leaf-list entries, each of which is
uniquely identified by one or more key leaves
container node - contains a grouping of related nodes that have only child
nodes, which can be any of the four node types
Access the Data Models
You can access the Cisco IOS XR native data models from GitHub, a software development
platform that provides hosting services for version control.
You can also access the supported data models from the router. The router ships with the
YANG files that define the data models. Use NETCONF protocol to view the data models
available on the router using ietf-netconf-monitoring request.
-oper in the model name indicates an operational model. For
example, Cisco-IOS-XR-invmgr-oper.yang is an operational
model for inventory data.
-cfg indicates a configuration model. For example,
Cisco-IOS-XR-controller-OTU-cfg.yang is a configuration
model for OTU.
Communication Protocols
Communication protocols establish connections between the router and the client. The
protocols help the client to consume the YANG data models to, in turn, automate and
programme network operations.
YANG uses the Network Configuration Protocol (NETCONF) .
The transport and encoding mechanisms for theis protocol are shown in the table:
Protocol
Transport
Encoding/ Decoding
NETCONF
ssh
xml
tcp
json
NETCONF Protocol
NETCONF provides mechanisms to install, manipulate, or delete the configuration on
network devices. It uses an Extensible Markup Language (XML)-based data encoding for the
configuration data, as well as protocol messages. You use a simple NETCONF RPC-based
(Remote Procedure Call) mechanism to facilitate communication between a client and a
server. To get started with issuing NETCONF RPCs to configure network features using
data models, see
.
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