The issues of double NAT mean nothing but troubles. When we see such a setup we will not offer support or fixes (I'm on a team of folk that work network and more issues.) We have to get the OK to convert it to a normal setup. If the client needs the second router for its WiFi we configure the router as a WAP and it works great.
I have 2 routers. One of which was provided by my ISP and essentially just sits in the living room as a modem in bridge mode. My other is an aftermarket router which has been flashed with DD-WRT, Linksys EA6500v1, if that's of any relevance.
I have a 50ft Ethernet cord running through the wall outlets into my room, powering my DD-WRT router's WAN port to create an unrestricted, full speed PPPoE connection of its own. This router is used for all Wi-Fi devices and nearby Ethernet devices, essentially acting as a primary Gateway router.
However, I have a desktop computer located in the living room where the ISP router is, and the only way it can get an internet connection is by hooking it up to the ISP router via Ethernet, also establishing PPPoE. As you can imagine, this creates various problems. I'd like to avoid having to buy a Wi-Fi card for it, as the wireless connection gets heavily degraded in that particular room.
What adjustments must be done to both routers that would allow me to somehow have this desktop computer hop over from the ISP router to my DD-WRT one? Perhaps I should look into LAN-to-LAN?
The firmware of my ISP router is highly limited, meaning that I have little options to do things such as create static routes on it.
I'm already anticipating that I'll have to reclarify my issue many times as/if this thread moves forward. Thank you so much for taking the time to read this and maybe even replying with your two cents.