My network setup causes issues

[Sandro797]

Here's my network setup. From modem (Calix 813-2g) 1 cable goes to TP-Link WR940N (for downstairs usage) and the other to IPTV STB.  from 940N, the cable goes to TP-Link WR841N (for upstairs usage), which is connected to PC via Ethernet cable. For 3 years the cable from 940N was plugged into the WAN port of 841N. About 2 weeks ago, I asked on this forum how to connect to my TV which is connected to 940N and followed an advice to plug the internet cable (coming from 940N) into LAN port on my 841N router. Before doing so, the settings of 940N showed that IP adress was my actual external IP. After switching the plugs on 841N, for some reason 940N shows internal IP as its IP. Also, I am now able to access Calix modem from my PC. Now my external IP is shown only in Calix's settings. I have some issues in games after cable switch and I had to search the web to solve this issue. 1 thread suggests that I should disable NAT on Calix or enable bridge mode, however, there is no such function there (searched for it as well). Also tried to plug ethernet cable from Calix into LAN port of 940N, but it did not work. I even enabled DMZ on calix for 940N. I am out of ideas and I need your help. Why did the settings change on 940N so that now it shows internal Ip instead of external? How to avoid Double NAT?

[myselfolli]

Okay first of all, I did in no way understand what your network setup looks like, I even tried drawing a picture:

 

If this is close to correct, please say so or go ahead and draw one yourself, your network description is incomprehensible. And where does Calix come into play? I am confused

[Sandro797]

@myselfolli Your drawing is correct. Modem itself is Calix 813-2g.

[myselfolli]

Mate, I am lost on what your problem is and what I can do to solve it. Please draw me some pictures, I've been trying to wrap my head around your problem for the better part of the last 20 minutes...

[Sandro797]

@myselfolli Added picture to the original post.

[Sandro797]

Earlier, the internet cable from 940N was plugged into WAN port of 841N. However, this way I was not able to cast anything to my AndroidTV from my PC, so I plugged the internet cable into LAN port of 841N and it solved my problem. So I had double NAT of 841N and 940N. Earlier, when I logged into 940N gateway, the IP address there was my external IP, given by ISP. For some reason, after I plugged internet cable into LAN port of 841N, gateway page of 940N shows that my IP is now 10.0.0.2. As far as I understand, I still have double NAT, but this time with Calix modem and 940N. This causes connection issues in some online games. Is there anything I can change in configuration of either routers or modem, so I keep the ability to cast to TV from PC and eliminate connection issues?