Which of the following is true about SNMP configuration?

The assertion that a managed device resides on a managed network and has a software agent is correct because, in the context of SNMP (Simple Network Management Protocol), a managed device is defined as a network node that is monitored and managed using SNMP. This typically includes routers, switches, servers, and other hardware that can communicate with a system for monitoring purposes.

A software agent resides on the managed device and is responsible for collecting data about the device's state and performance, and it also receives and processes commands from the SNMP manager. This agent acts as the intermediary, facilitating communication between the managed device and management systems. Therefore, the combination of a managed device being part of a managed network, along with having a software agent installed, is a fundamental aspect of SNMP configuration and architecture.

The other options do not accurately reflect how SNMP operates within a network environment. For instance, managed devices must have agents for effective SNMP communication, and simply configuring monitoring applications without addressing the managed devices themselves would lead to incomplete or inadequate monitoring strategies. Furthermore, SNMP configuration is essential for the function of devices that need to be monitored; it is not optional in a typical managed network setup.