Which two tools require a software agent to be installed on all devices you want to manage?

The correct choice emphasizes the need for a software agent on the managed devices, which is a key characteristic of both Chef and Puppet. These are configuration management tools designed to automate the deployment and management of applications and systems. They require an agent installed on each device to facilitate communication and execute tasks. The agent is responsible for applying the defined configurations and reporting back to the management server.

In contrast, Ansible and Saltstack can operate in an agentless mode, allowing them to manage devices without requiring an agent. Instead, they often leverage existing protocols like SSH to communicate with the devices, which differentiates them from Chef and Puppet.

NETCONF and RESTCONF are protocols used for network configuration and management but do not inherently require a software agent, as they can work over standard communications mechanisms. YANG and JSON are data modeling languages and formats that are not directly involved in the management of devices, and thus do not pertain to the requirement of having software agents installed.