My main router is a TPLink (192.168.1.1) in which is connected a openWRT router working in AP mode (LAN 192.168.1.253, WAN 192.168.4.1). I can connect to openWRT, use the internet and ping machines under in any part of the network (192.168.1.x or 192.168.4.x). The problem is I can't ping from any machine in the 192.168.1.x network to machines in the 192.168.4.x one. I tried dealing with firewall (even turning it off), masquerading and so on.
To confirm that at least I am inputting the right data to the router (TP_Link):
You took it one step further. What I meant was to keep it as a router, but eliminate the firewall factor by placing both wan and lan in the lan zone.
If routing is not indeed needed, then your suggestion for converting into a dumbAP is certainly the best for this usecase.
@ebiscaia - what is your goal for this device? Do you specifically want different subnets, or just how it is currently setup? As others have stated, a dumb AP is an easy solution for your issue, but may or may not be what you want. Can you give us a description of your goals?
IMO, this is a good reason to use a different subnet like this. There are other ways you could achieve the same end result (such as replacing your main router with one running OpenWrt and then using VPN policy based routing), but this one is perfectly valid.
That said, if you have a VPN running, you may need to do VPN-PBR anyway in order to allow the local traffic between your two subnets. That may be the reason you were having issues in the first place.
I think you can probably close this thread and start a new one if/when you have issues or want to change the topology.