NETCONF and YANG

NETCONF is a network management protocol (RFC 6241) designed to replace CLI-based configuration. YANG is the data modelling language (RFC 7950) that defines the structure of network configuration and operational data. Together, they provide a model-driven, programmatic approach to network management.

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The Problem with CLI

Issue	CLI	NETCONF + YANG
Data format	Unstructured text	Structured XML (or JSON)
Parsing	Regex, screen scraping	Standard XML/JSON parsing
Transactions	No atomic transactions	Commit/rollback support
Validation	Device checks after apply	Schema validation before apply
Consistency	Vendor-specific commands	Standard protocol, model-driven
Error handling	Parse text for error messages	Structured error responses

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NETCONF Overview

What is NETCONF?

NETCONF (Network Configuration Protocol) is an IETF standard for installing, manipulating, and deleting network device configurations:

Feature	Description
Transport	SSH (port 830 by default)
Encoding	XML
Operations	get, get-config, edit-config, copy-config, delete-config, lock, unlock, commit
Datastores	running, candidate, startup
Capabilities	Server advertises supported features during session setup

NETCONF Layers

┌──────────────────────┐
│     Content          │  ← Configuration and operational data (XML)
├──────────────────────┤
│     Operations       │  ← get, get-config, edit-config, commit, etc.
├──────────────────────┤
│     Messages         │  ← RPC request/reply framing
├──────────────────────┤
│     Transport        │  ← SSH (secure, authenticated)
└──────────────────────┘

NETCONF Operations

Operation	Description
<get>	Retrieve running configuration and operational state
<get-config>	Retrieve configuration from a specific datastore
<edit-config>	Modify the configuration
<copy-config>	Copy one datastore to another
<delete-config>	Delete a datastore (not running)
<lock> / <unlock>	Lock a datastore to prevent concurrent edits
<commit>	Apply candidate configuration to running
<validate>	Validate the candidate configuration
<discard-changes>	Discard changes to the candidate datastore

Candidate vs Running Datastore

                          ┌─────────────┐
edit-config ──────────>   │  Candidate  │
                          │  Datastore  │
                          └──────┬──────┘
                                 │
                           commit │
                                 ▼
                          ┌─────────────┐
                          │   Running   │
                          │  Datastore  │
                          └─────────────┘

The candidate datastore lets you stage changes, validate them, and then commit atomically. If something is wrong, you can discard changes without affecting the running configuration.

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YANG Overview

What is YANG?

YANG (Yet Another Next Generation) is a data modelling language that defines the structure and constraints of network configuration and state:

Feature	Description
Defines schema	What configuration options exist and their data types
Hierarchical	Tree structure with containers, lists, and leaves
Constraints	Mandatory fields, valid ranges, patterns, when conditions
Reusable	Modules can import and augment other modules
Vendor-neutral	OpenConfig models work across vendors

YANG Model Types