📘CCNP Encore (350-401-ENCORE-v1.1)
1. What Is YANG?
YANG (Yet Another Next Generation) is a data modeling language used to describe how network devices store, organize, and exchange configuration and operational data.
In simple terms:
- YANG defines the structure of data
- It does not configure the device itself
- It acts as a template or blueprint that network devices and controllers understand
YANG is mainly used with:
- NETCONF
- RESTCONF
These protocols use YANG models to read and write data on network devices.
2. Why YANG Is Needed
Traditional device configuration:
- Uses CLI commands
- Is vendor-specific
- Is hard to automate
- Can be inconsistent across devices
Modern networks require:
- Automation
- Programmability
- Standardized data formats
- Controller-based management
YANG solves these problems by:
- Providing a standard way to describe device data
- Allowing automation tools and controllers to work consistently with devices
3. High-Level Principles of YANG
3.1 Data Modeling (Not Configuration Language)
A key principle:
YANG models describe data, not commands
YANG defines:
- What data exists
- How data is organized
- What values are allowed
- Relationships between data
It does not:
- Execute actions
- Run CLI commands
3.2 Structured and Hierarchical Data
YANG uses a tree-like structure, similar to folders and files.
- Top-level nodes → major features
- Child nodes → sub-features
- Leaves → actual values
This structure:
- Makes data easy to understand
- Allows consistent navigation of device data
- Helps automation tools know where data belongs
3.3 Separation of Configuration and Operational Data
YANG clearly separates:
- Configuration data (settings applied to a device)
- Operational/state data (live status and statistics)
Examples:
- Configuration: Interface IP address
- Operational: Interface up/down status, packet counters
This separation:
- Improves clarity
- Prevents accidental modification of live data
- Helps monitoring systems
3.4 Data Validation and Constraints
YANG supports rules and limits for data values.
It can define:
- Allowed value ranges
- Mandatory fields
- Default values
- Data types (string, integer, boolean)
This ensures:
- Invalid data is rejected
- Devices remain stable
- Fewer configuration errors
3.5 Reusability and Modularity
YANG supports:
- Modules (main data models)
- Submodules (smaller reusable parts)
- Groupings (reusable data structures)
This allows:
- Vendors to reuse models
- Engineers to build consistent designs
- Easier maintenance and updates
3.6 Vendor-Neutral and Vendor-Specific Models
YANG supports two model types:
Standard (Open) Models
- Defined by standards bodies (IETF)
- Work across multiple vendors
- Common features shared by many devices
Vendor-Specific Models
- Extend standard models
- Add unique vendor features
- Used when advanced or proprietary features are needed
This gives:
- Flexibility
- Interoperability
- Standardization where possible
3.7 Protocol Independence
YANG is independent of transport protocols.
It can be used with:
- NETCONF (XML)
- RESTCONF (JSON)
- gRPC (model-based APIs)
This makes YANG:
- Future-proof
- Compatible with modern APIs
- Suitable for cloud and controller environments
4. Benefits of Using YANG
4.1 Standardized Network Management
YANG provides:
- A common data language
- Predictable data structure
Benefits:
- Easier integration with controllers
- Reduced vendor lock-in
- Consistent automation scripts
4.2 Enables Network Automation
Automation tools rely on:
- Structured data
- Predictable models
YANG enables:
- Programmatic configuration
- Bulk changes
- Repeatable deployments
Result:
- Faster operations
- Fewer manual errors
- Scalable networks
4.3 Improves Reliability and Accuracy
Because YANG enforces:
- Data types
- Value limits
- Mandatory fields
It helps:
- Prevent misconfiguration
- Detect errors early
- Maintain network stability
4.4 Easier Integration with Controllers and APIs
YANG works naturally with:
- SDN controllers
- Network management systems
- DevOps tools
Controllers:
- Read device capabilities using YANG
- Push validated configuration
- Collect real-time operational data
4.5 Clear Documentation of Device Capabilities
A YANG model acts as:
- A machine-readable manual
- A precise description of supported features
Benefits:
- Engineers know exactly what a device supports
- Tools can discover capabilities automatically
- Less guesswork and manual checking
4.6 Scalability for Large Networks
In large environments:
- Manual configuration does not scale
- CLI becomes slow and error-prone
YANG enables:
- Centralized control
- Consistent configurations
- Easy expansion of the network
5. YANG in an IT Environment (Conceptual Example)
In a modern IT environment:
- A network controller manages hundreds of devices
- The controller uses YANG models to understand device data
- Configuration is sent using NETCONF or RESTCONF
- Devices validate data using YANG rules
- Operational data is collected in real time
This approach:
- Reduces manual work
- Improves visibility
- Supports automation and orchestration
6. Key Exam Points to Remember
For the CCNP ENCOR exam, remember:
- YANG is a data modeling language
- It defines structure, not commands
- Uses hierarchical data models
- Separates configuration and operational data
- Supports validation and constraints
- Works with NETCONF and RESTCONF
- Enables automation and programmability
- Supports standard and vendor-specific models
7. Simple Summary (For Quick Revision)
- YANG describes how network data is organized
- It is used for programmable networks
- It improves automation, accuracy, and scalability
- It is essential for controller-based and API-driven networks
