What data modeling language is used by NETCONF?

NETCONF utilizes YANG as its data modeling language. YANG is specifically designed to model configuration and state data manipulated by network management protocols like NETCONF. It provides a structured way to define the data sent and received by these protocols, allowing for the representation of the hierarchical data structures necessary for managing network configurations.

YANG's design supports features such as modularity, which enables reusability of data models across different network devices and services. Additionally, it allows for the inclusion of constraints, documentation, and descriptions of data elements, enhancing the clarity and usability of network configurations.

While XML is commonly used as a transport format in NETCONF for sending messages, it is not the data modeling language employed. JSON, although it is another popular data interchange format, is not used in NETCONF for data modeling purposes. SMI, which stands for Structure of Management Information, is an older specification related to SNMP and not directly relevant to NETCONF operations or YANG.

Thus, YANG is the correct answer as it defines the structure and types of data that can be managed using the NETCONF protocol.