Do I use an Ethernet router or a switch with my DM32 for multiple fan tests?
Routers and switches are different kinds of networking equipment, and are not interchangeable.
A switch will for the most part just pass the traffic through. Switches can be used for multiplexing so you can get multiple inputs onto one output. They can also be used as signal boosters so you can extend the length of your data connection.
A router will dynamically generate IP addresses for devices connected to it. The router will also multiplex and boost signal.
When networking, it is important to understand what piece of equipment is in charge of generating the IP...