Accessing a Router Behind a Modem/Router With No Access To The Modem/Router

Question

The Problem:

Want to access a router (and devices connected to it) from outside, which is behind a modem/router which i have no access to its admin page and has no port open but 80.

The Story:

Problems began 6 months ago when i changed my ISP from Rostelecom To Ucom. After signing up for their service they forced my to use their free fiber optic modem which had WiFi and 4 LAN ports on it which was okay at the beginning. One day i decided to change my WiFi SSID and Password. Went to 192.168.6.1 and tried to login in it by any possible default user/pass combination but it didn't went anywhere. I called my ISP customer service and ask for the user/pass, but they replied that you can't apply any changes into that modem because it's our property and we're not allowing users to login into for "security reasons". Anyways i was okay with it because it was pretty cheap (40Mbps for $15/month). Then i decided to run a file server on my linux server, and as i knew that they wont give me the user/pass i called them again and asked them to port forward FTP/Samba ports to my linux server IP, they mentioned "Security Reasons" 3 times and suggested to buy a Router/Access Point to do the port forwarding on it. Bought the router, installed it, config'd it, and instead of port forwarding the ports one-by-one, DMZ'd it. But it didn't work... called 'em explained what i wanna do and after 2 hours of talking to their "IT Technicians" they finally suggested me to buy static IP from them for $2/month and they didn't had any clue why it does not work...

Answer 1

If their internet modem does NAT/PAT then there is no way to have any device sitting behind the modem be accessible from the internet without modifying the config in that modem.

You will have to buy your own modem/router and toss theirs. Your modem/router would pull dhcp from the internet and then you'd NAT on that device. Essentially your just replacing their modem/router with a modem/router that you have the password too. Ive done this with a cisco router at my house with charter. But ive heard some ISPs will only work with certain devices, not sure how accurate that is.

Its not a security issue for their modem to forward the ports to your server, thats how every server on the internet is connected. Worst case scenario would be your server getting compromised which wouldnt affect their modem what so ever. My assumption is that the support staff your talking to have little to no technical knowledge and dont really understand what your asking.