Networking options will depend on the brainboard(s) being used.
Multiple boards with Ethernet
If you want to run multiple brainboards with Ethernet you’ll need to provide multiple ethernet ports and cables. Each brainboard functions as an individual entity and do not share connections or configurations.
Amazon and Aliexpress both sell cheap switches you can use to hook up multiple brainboards!
POE Networking and Standby power
Sometimes you might want to run a box remotely and don’t want to run to many cables but having a switch locally connected to AC would be prohibitive. In this case you could run a POE powered switch which in turns also feeds the brainboards with standby power. Please see this dedicated article for more details!