📘 CCNA 200-301 v1.1
6.3.b Northbound and Southbound APIs
In modern networks, especially in controller-based networks and Software-Defined Networking (SDN), devices like switches and routers are controlled by a central software component called a controller. The communication between the controller and other parts of the network uses APIs (Application Programming Interfaces).
APIs are like “messaging systems” that allow software to talk to each other. In SDN, we have two main types of APIs:
1. Southbound APIs
- Definition:
Southbound APIs are used by the controller to communicate with network devices (switches, routers, access points, etc.).
In other words, they “go downwards” from the controller to the devices. - Purpose:
They allow the controller to configure, manage, and monitor network devices. The controller can push policies, routes, and network instructions directly to devices. - Common Southbound APIs/Protocols:
- OpenFlow: Lets the controller tell switches how to forward traffic.
- NETCONF/YANG: Used for configuring devices in a structured way.
- SNMP (Simple Network Management Protocol): Used for monitoring network devices.
- Example in IT context:
A controller decides how traffic should flow in a data center network. Using a Southbound API like OpenFlow, it tells a switch exactly which path to use for data packets.
Key Point: Southbound = Controller → Network Devices
2. Northbound APIs
- Definition:
Northbound APIs are used by the controller to communicate with higher-level software applications (like network management tools, orchestration software, or monitoring dashboards).
They “go upwards” from the controller to software applications. - Purpose:
They allow applications to retrieve network information (like traffic statistics or device status) and sometimes send instructions to the controller. - Common Northbound APIs:
- RESTful APIs: Most common type; applications can use HTTP requests (GET, POST, PUT) to interact with the controller.
- JSON/XML-based APIs: Data is often returned in structured formats like JSON or XML for applications to understand.
- Example in IT context:
A network monitoring application queries the controller through a REST API to see which switches are overloaded. It then uses this information to generate alerts.
Key Point: Northbound = Controller → Applications
Summary Table for CCNA Exam
| Feature | Southbound API | Northbound API |
|---|---|---|
| Direction | Controller → Network devices | Controller → Applications |
| Purpose | Configure and manage network devices | Provide network info to applications |
| Common Protocols/API | OpenFlow, NETCONF, SNMP | REST API, JSON, XML |
| Example | Controller tells switch paths for traffic | Monitoring app queries network stats |
Important Notes for the Exam
Together, these APIs make SDN networks programmable and centralized, which is what differentiates them from traditional networks.
Southbound APIs directly control hardware.
Northbound APIs directly communicate with software applications.
