OpenWrt as both dumb AP AND router

[dimasblackboy]

Hello, everyone!

I've recently bought a TL-MR3020v3 and flashed the latest openWRT version to it. Pretty satisfied.
It is a single-port device which is now configured as a WAN port.
It was intended to be used as a travel router and it works wonders at that particular purpose.
I've just discovered that one of the clients I wish to connect to it needs an IP from the upstream router (so I would need to use the router as a "dumb AP").
I do not want to lose my own original subnet by setting it as an bridged AP, though.
So, here is the question: can I set up both bridged AP and router modes in the same device and therefore use the same eth as LAN and WAN?
How feasible would that be?

[psherman]

It is possible, but you will likely need to make a few changes.

You'll need to create a bridge for the wan -- call it br-wan and it will contain eth0. Then, you change your wan network interfaces to use device br-wan. Finally, setup a second SSID and associate it with the wan network. This should allow the second SSID to be a dumb AP on the upstream network, while the original SSID will be firewalled/NAT'd based on your existing configuration.

If that doesn't work, please post your config files:

Please copy the output of the following commands and post it here using the "Preformatted text </> " button:

Remember to redact passwords, MAC addresses and any public IP addresses you may have:

cat /etc/config/network
cat /etc/config/wireless
cat /etc/config/dhcp
cat /etc/config/firewall

[dimasblackboy]

Thanks for the answer!
Alongside that should I also follow the instructions on the "dumb AP" guide, such as turming off dnsmasq for the 2nd SSID etc.?

[psherman]

by default, the DHCP server on the wan interface is set to 'ignore' so you should be fine.