One of my co-workers once saw a device that plugged into a RJ45 jack, that emulated a PC. It could be configured with an IP address, and respond to pings.

I was wondering if anyone knew about these, or even what they are called?

This will be used to simulate a PC in a classroom environment.

Thanks in advance.

Edit: This is a CCNA classroom, we are looking to simulate a PC connected to an ethernet port on a router. These will be on different subnets, etc. This might be doable with a VM through VLANs and virtual switches, but then we are getting away from configuring the physical ports on the router the way we want to.