Port forwarding and DDNS

Hello world.
I'm new here.
i'm struggling with problem with port forwarding.
I can't forward any port (doesn't work) to my devices and I don't know why.
My config:
ISP router (4G one): IP, disabled DHCP, hidden WIFI.
Main router (TP Link MR3400): WAN IP:, LAN IP:, enabled DHCP, connected to ISP router via WIFI, acts as an AP with enabled SSID broadcast and has configured DDNS (URL update).
I want to forward certain ports from main router to devices connected to it either via cable or WIFI.
My main goal is to use DDNS to connect to those devices.
Can someone help?

Devices connected to the main router just need port forwarding working on the main router. You should ask for support to your ISP.

That is LAN, but what is your WAN address? I guess you have private IP there, so you have nothing to forward as you're not reachable from Internet. No relation to OpenWrt yet.

I use cellular data as internet source so my public IP changes everytime the router restarts (or after 24h).
Becuase of that I set up DDNS to reach my devices.
Now I'm looking for a way to access my devices via:
And my relation to OpenWrt is that on the main router (TP-Link) I've got Lede installed.

Do you really have one on your router? Can you show a proof from your router?

After quick research I found out that my ISP assings private IP but just to know it.
On which router and how should I forward ports:
ISP Router -> Main Router -> Device
should I forward like this: Main Router -> Device?

then forget about port forwarding and DDNS, please re-read my 1st answer

But I want to know how to properly forward if my ISP (of course for additional payment) assigns me public IP

If they will give you a public (routable) IP address (i.e. assign it to 'ISP Router' WAN interface) you will need to put into DMZ of 'ISP Router', then on 'Main router' you will need to add the rules you need in Firewall - Port Forwards.
Alternatively you can use your 'Main router' as Dumb AP and configure the forwardings on 'ISP Router'.

thanks that helped a lot.

My device is having issue when i am connecting to the office wifi, can any one tell why?

@mukulb, welcome to the community.

Given that your question appears totally unrelated to the OP's DDNS issue, please make a new thread to discuss your problem. Be sure to provide details, device model, OpenWrt version, etc.

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