Hi, first of all let me tell you that i'm a noob with networks and also that English is not my first language. I'll try to explain it with words, but I also have some images
Until now, I've used an old router as a switch (i think) to plug different devices in my room, and then I use a PLC to connect this router to the ISP's in the living room.
To do this, I changed the ISPs router IP from 192.168.0.1 to 192.168.1.1 and my other router to 192.168.1.2
I also opened some ports in the ISP router to my devices and assigned some manual DHCP leases.
This works well, but the ISPs router web interface is crappy and limited and sometimes doesn't work, so I want to restore it to .0.1 and make my router .0.2 on one end ant 1.1 on the other and then put all my devices in .1.0/24
Right now in the LEDE router I have this (just restored it)
I am unsure why you have configured your network as you have, because a router acting as a switch is essentially useless.
However, to make your router act as a router, you will need:
Reset it to default settings, so that you have a green LAN zone and a red WAN zone (you can set this up manually but if something will be wrong, there will be too many things to check)
Set WAN interface to protocol DHCP (this should be set by default)
Set LAN interface IP address to 192.168.1.1 and turn on DHCP server on it (this should also be set by default)
Connect your ISP router to your router's WAN port (associated with red WAN zone; this I assume is what you did not do last time)
Connect your computers to the LAN ports (associated with green LAN zone; this should be by default)
Might also pick up a good book on networking and check what a router is for while you're at it.
As I've said I have a PLC going from the ISPs router in the living room to my bedroom. It only has 1 port, so I used a refurbished DSL router as a switch to have 3 more.
That's my problem. My router doesn't have the WAN interface (it's an AR-5381u). The physical ones are the ADSL line and 4 LAN.
So I need instructions how to create the WAN interface
In your new scenario, each router does its own NAT by default, and the devices behind your LEDE router will get double NAT for their internet access. It mostly works, but is undesirable.
Would it be an option for you to replace the ISP's router with another LEDE router? This is the place where you can see the largest improvement by switching to LEDE. The device in your room could then stay in switch mode (access point), and double NAT is avoided.
@jeff, since @LoLo2207 is using a powerline link between the rooms, I assumed there is considerable wifi signal attenuation between them, and it is not possible to provide wifi coverage in the living room from the LEDE access point in the bedroom.
The device wiki page explains how to configure the switch to change one of the Ethernet ports into a WAN port. https://openwrt.org/toh/comtrend/ar5381u
If there is signal at the router location, it may also be possible to make the device a wifi client of the main router, achieving the WAN link over wifi.
It requires a static route to the LEDE network on the ISP router. And it also needs to NAT traffic from the LEDE router with a destination on the internet. Unfortunately these features aren't available on all routers.
There's a nice explanation of how the switch can be used to create a WAN port where the device has none. The link you have previously already contains the steps how to do it, this article just contains a nicer explanation: https://wiki.openwrt.org/doc/uci/network/switch
