Q:

How prevent access to a device (192.168.1.102) from others devices than the one I allow (192.168.1.100) if the 192.168.1.102 don't have firewall

I have some devices that don't have firewall neither can't have, it's like an arduino, more specifically its a esp8266 with "ESP-Easy" Firmware.
And what i want/need is to only a certain computer be able to access it. like this:

1# ESP8266 board with ip 192.168.1.102
2# Computer with ip 192.168.1.100
3# Any other Device with a unknown IP address

2# is abble to communicate with 1# and vice versa 
3# is able to commumnicate with 2# but NOT with 1#

How can i archieve that if 1# have no firewall. I thought how about my router firewall that have OpenWrt installed...  but how?
What's type of rule i need or what rules i need

A:

There is no secure solution to this if the devices are on the same LAN. Nodes on the same network talk directly to each other, there is no way to divert the traffic via an firewall. You will have to put the computer and the board on a separate LAN, with a firewall between the LANs. A cheap, but insecure, solution is to add a second IP address to the network interface on the computer, say 10.0.0.1/30, and give the board address 10.0.0.2/30. This way they are on the same physical network, but are using a different subnet.

