Each eero has two Ethernet ports. One of the Ethernet ports is used to connect your gateway eero to the Internet via your modem. The other Ethernet port can be used to hardwire another device (such as a Sonos player) directly to your network. If you’re using more than one eero, you can also use the Ethernet ports to wire eeros together. It doesn’t matter which Ethernet port you use to connect to your modem since eeros configure themselves automatically.
There are a few differences between the 1st and 2nd-generation eero.
The 1st-generation eero has a pin-hole style reset button, a barrel-style 12v power adapter, two Ethernet ports, and a USB 2.0 port. The USB port on the back of eero is only for diagnostic purposes, so do not plug any devices like printers into your eero's USB port.
The 2nd-generation eero has a reset button, a USB-C 12v power adapter, and two Ethernet ports. Just like the 1st-gen eero, the USB-C port on the 2nd-gen eero should only be used for its purpose, which in this case is powering your eero.