Problem with accessing we server outside the LAN

Hi,

I'm having a problem with my new modem router I just bought recently - billion bipac 7800N. The problem is I can surf the net and access to my website internally on my LAN, but not when outside of the network.

By the way, I'm hosting my own web server. The way I got this done is through the use of subnet 8 static IP addresses serviced from my ISP provider.

Anyway, here is my network topology

My modem router - billion 7800N is connected with both my web server machine and a router Netgear FVS318 which connects all my PCs on the LAN network.

My modem router is assigned with IP address of say 121.35.2.21
My web server is assigned with 121.35.2.23
My Netgear router is given with 121.35.2.24
After configuring my new modem billion 7800N with the right settings given by my provider, I got my Internet working from my laptop which has static IP address of 121.35.2.22 at the office. I was able to open my website with no problems. I thought all was all right.

When I was at home, I happen to check again to see if I can access to my web server but to my surprise, I could not get my webpage loaded on my Firefox.

Now, I have done port forwarding through port mapping under the virtual server in billion 7800N to let port 80 through to 121.35.2.23.
I have also disabled the NAT on my billion and left the NAT on the Netgear router enabled. Usually from my experience, this should work.

I must tell you though that my web server runs on Ubuntu server 12.08 which is set up with iptables.

So I have run out of ideas as to how to solve this problem.

Any help would be greatly appreciated.

Thank you