Hi.
I have a doubt about port forwarding passing through 2 different routers.

The company I work used to have a modem connected to a tp-link router. The router was responsible for authenticating in the internet and the wireless network (that means the modem was configured in bridge and the router in PPPOE). To be able to use a special VNC application, I had to configure a port forwarding in this router, where any connection from the internet that came to port 1101 would be redirected to the 192.168.1.101 internal ip address. That worked just fine.

We moved to a new place and changed the internet provider. The new Internet provider supplies a router that authenticates the internet, sets a fixed ip address for the company, etc.
So, I still use my tp-link wireless router, but instead of setting it to PPPOE, now it's set to DHCP (with reserved ip address for the tp-link router 192.168.0.5).
Everything is working perfectly, except the port forwarding. That is what I need your help to fix.

What I did:
- Reserved the ip address 192.168.0.5 for the tp-link wireless router in the settings of the Internet provider's router. Both of them connected through a ethernet cable.
- In the settings of the Internet provider's router I configured a port forwarding in its settings saying that any connection from the Internet in the port 1101 should be redirected to the tp-link router in the 192.168.0.5 ip address, with both inbound and outbound ports as 1101.
- In the TP-link router, I maintained the previous port forwarding that established that any connection that the router receives in the port 1101 should be redirected to the machine 192.168.1.101 (the same setting that was configured before and that worked).

The problem is that it didn't work. Something is wrong and I don't know what it is. I suspect that the Internet Provider's router, when it redirects the connection that it receives in the port 1101, it just redirects it to the tp-link router without the port 1101 information. If that's true, that would explain why the second and last/final port forwarding is not working in the tp-link router.

Just one obvious information, before anyone asks: I can't configure the port forwarding the Internet Provider's Router settings directly to the ip 192.168.1.101, because it's not a network that the router can "see". It doesn't accept any ip address other that 192.168.0.xxx (mask 255.255.255.0).

Can any of you imagine where I am doing things wrong?
Thank you

This article talks about exactly what I am doing in my network and his logic and way of configuring the routers is exactly the same that I did. The only difference is that mine is not working.
He named that DOUBLE ROUTER FORWARDING.

The obvious question but I assume you have verified that the ISP MODEM is plugged into the WAN port of the TP-Link router. As far as I know it should work.

You might be able to configure the ISP router in a bridged mode which basically bypasses its router functions and then the TP-Link would work like your old network. In addition you might be able to configure the ISP router LAN IP address and range to match your old network so the TP-Link is not required anymore.

Both would eliminate the need for double NAT.