Which feature must be configured before implementing NetFlow on a router?

NetFlow is a Cisco IOS application that provides statistics on packets flowing through the router. NetFlow is based on 7 key fields that identify a flow, such as source and destination IP addresses, source and destination port numbers, layer 3 protocol type, ToS byte, and input logical interface. To enable NetFlow on a router, IP routing must be configured first, because NetFlow relies on IP addresses to classify and monitor traffic. SNMPv3, syslog, and VRF are not required for NetFlow configuration, although they can be used for other purposes such as network management, logging, and virtualization. References:

Getting Started with Configuring Cisco IOS NetFlow and NetFlow Data Export (Section: NetFlow Data Capture)

How to configure NetFlow on Cisco routers (Section: Enable NetFlow)

Implementing and Operating Cisco Security Core Technologies (SCOR) v1.0 (Module 5.1.1)