networking – Raspberry pi with ubuntu: Forwarding all traffic from one interface to another

I have two Raspberry Pis running Ubuntu. Both of them have a native ethernet port and a usb ethernet->usb interface. They are both connected with their native ethernet to the same router. I want them to forward all traffic from their usb interfaces to the ethernet port. Is this possible with something like iptables? I’ll try to illustrate with a table below.

RBP1 RBP2
traffic usb1 <–> eth0 router eth0 <–> usb2 traffic

So traffic in goes to usb1 which just throws everything out eth0, everything from eth0 gets thrown out usb1. Same thing on the other RBP.