Which type of API is being used when a security application notifies a controller within...

 A security application that notifies a controller within a software-defined network architecture about a specific security threat is using a northbound API. A northbound API is an interface that enables communication between the SDN controller and the applications or management systems that use the network services1. A security application can use a northbound API to send alerts, requests, or commands to the SDN controller, which can then take appropriate actions on the network devices or policies2. For example, a security application can use a northbound API to inform the SDN controller about a malicious traffic pattern, and the SDN controller can then block or redirect the traffic using a southbound API3.

 1: What is Software-Defined Networking (SDN)? | VMware Glossary 2: Intent-Based Networking’s Next Evolution: The DNA Center Platform - Cisco Blogs 3: Cisco SDN Security: Securing the Software Defined Network - Cisco