A northbound interface (NBI) connects the Application Layer with the Control Layer in software-defined networking. Applications communicate network requirements and desired behavior to the SDN controller through the NBI; the controller translates those high-level requirements into instructions for network devices. section 22.2.2 section 22.4
Key points:
- Typically uses a representational state transfer (REST) API with HTTP messages. section 22.2.2
- Differs from the southbound interface (SBI), which connects the Control Layer to the Infrastructure Layer. section 22.2.2
- Leaves device execution to the Infrastructure Layer after the controller produces actionable instructions. section 22.4
Figure 22.6 The three layers of SDN architecture: Application, Control, and Infrastructure. The NBI facilitates communication between the Application and Control Layers, and the SBI facilitates communications between the Control and Infrastructure Layers.
The layered SDN architecture places the NBI between applications and the controller, while the SBI connects the controller to network infrastructure. section 22.2.2
