I am writing a simple chat program based on a client-server model.

The server listens to port 33000 and uses TCP.

When both client and the server are in the same LAN created with Archer A6 everything works fine.

That is the server is running on my desktop which has wire connection to the router and the client is running on my laptop which is connected to LAN via wifi.

I open the client and connect to the IP of my desktop in the LAN. Again, everything works.

Now, NAT comes in play when I want to make the server accessible from the Internet.

I used this official guide to set up my Archer A6. That is, NAT Forwarding->Virtual Servers-> I created new Service Type, set external and internal ports to 33000 and internal IP to IP of my desktop in LAN, protocol to TCP. Also I did not forget to enable the entry in the settings.

From my laptop I connect to the Internet via my phone's wifi hotspot.

Then I tried to open the client and connect to the WAN IP of my Archer A6 (I got the IP from the tplinkwifi.net, it is dynamic) and there was no result. Connection timed out.

Desktop OS: Ubuntu 20.04

Laptop OS: Ubuntu 18.04.

iptables are emtpy (only accept policies), no firewall enabled.