The reason "bridge" is on quotes is because I don't know if that is what I really need or if it is possible to do.
I have a device with an Ethernet port, a Siemens PLC, s7-300.
I want to plug it to my Raspberry 3b+, and connect the Raspberry to an existing Wifi on my network, so I can communicate with the PLC.
Or plug it, and then create a "dumb" AP with the Raspberry and connect another device on the same network via Wifi to the rasp, so everything is connected and networking.
What I mean by dumb is that I don't want the Raspberry to act as a DHCP server, I already have a router that deals with that and I do not want it to interfere.
I have tried a lot of guides i found on google but nothing works, the best i could get was creating the AP so if i plug the pi to the router by LAN, it gets internet connection and the Wifi of its AP give internet to the devices connected to it, but i can only ping devices from Wifi to LAN, I can't ping from a device connected by LAN to one by Wifi.
PLC----Rasp via cable. Rasp------Existing SSID. or Rasp AP----- Some computer on the same network receives it
Is any of this possible?