heterogenous network with devices from different
vendors was almost impossible before NETCONF and
YANG data models were created.
YANG is a language used to model data for the
NETCONF protocol. A YANG module defines a hierarchy
of data that can be used for NETCONF-based operations.
It allows a complete description of all data sent between
a NETCONF client and server. YANG models the
hierarchical organization of data as a tree in which each
node has a name and either a value or a set of child
nodes. YANG provides clear and concise descriptions of
the nodes, as well as the interaction between those
nodes.
YANG strikes a balance between high-level data
modeling and low-level bits-on-the-wire encoding. The
reader of a YANG module can see the high-level view of
the data model and understand how the data will be
encoded in NETCONF operations.
YANG structures data models into modules and
submodules. A module can import data from other
external modules, and it can include data from
submodules. The hierarchy can be augmented, allowing
one module to add data nodes to the hierarchy defined in
another module.
A YANG module contains three types of statements:
Module-header statements describe the module and give information
about it.
Revision statements provide information about the history of the
module.
Definition statements are the body of the module, where the data model
is defined.