I hope someone can tell me how to move forward.
My goal is to use my newly aquired, openwrt-enabled, used TP-Link TD-W9980B as router before a cable modem as desribed here:
That is, as a first step I would like to keep the cable modem/router as it is (no bridge mode yet) and route all traffic from the LAN through the TP-Link to the cable modem into the internet and back (I worry about NAT problems later).
-A TP-Link TD-W9980B router with openwrt 18.06. I bought it used and preinstalled. I resetted it to default settings.
-My ISP is cable with a CBE CH6640E cable modem.
I configured the cable modem to use the 192.168.2.x address space. DHCP is still enabled, but should be disabled once everything is working. Also, WLAN is still enabled and will be disabled.
I configured the TP-Link to use the 192.168.1.x address space. DHCP is enabled.
My computers' Wifi is able to connect to the tp-link and is assigned a 192.168.1.x address. Also, I can access the web interface of openwrt by going to 192.168.1.1. So I think this part works, which is I believe the part under Network->Interfaces->LAN. That part is also green.
To make the router connect to the internet, I think I have to connect to the cable modem through eth. This has to be configured in the WAN part of Network->Interfaces so that the router is both in 192.168.1.x and 192.168.2.x networks, correct?
I tried several options but none worked and I'm not sure what I need to configure.
The router has 4 eth ports at the back, the first 3 are labeleld LAN1, LAN2, LAN3, the 4th is labelled LAN4/WAN. I'm not sure if that means that I HAVE to use the 4th eth port to connect to the cable modem. The cable modem uses both ipv4 and ipv6, I'm not sure which is used when and why.
The current Network->Interfaces->LAN configuration is:
Protocol: Static address with 192.168.1.1
Interface: eth0.1, wlan0
The current Network->Interfaces->WAN configuration is:
Protocol: DHCP client
VLAN ID 1
CPU (eth0): 1000baseT, full duplex, tagged
LAN1: No link, untagged
LAN2: No link, untagged
LAN3: No link, untagged
LAN4: 1000baseT, full-duplex, untagged
I think I have to configure here to use the LAN4 port as exclusively going to the cable router, but I don't know what I have to do for that.
In the end, I would like to change the routers SSID to the one of my current WLAN, disable the cable modems wlan, disable the cable modems dhcp so that everything works as before
Is that possible? Can anybody help me? I hope I supplied sufficient information.