DDNS Behind 2 Routers

Similar questions had been asked and I read through them all, however my problem still persists.

I have DSL modem/router (Billion brand, 192.168.0.xx) fed straight through an ASUS GX1005B unmanaged Ethernet switch to provide enough connections in Network 1 (N1), a Netgear router (192.168.1.xx) in Network 2 (N2), and a CCTV DVR I'd like to remotely monitor connected on N2. So the topology is: Internet -> DSL modem/router -> ASUS Switch -> Netgear Router -> DVR

In N1, the ASUS switch doesn't seem to have any admin page so I am making all the changes through the DSL modem/router admin page. In there, I am forwarding TCP/80 to Netgear (N2) WAN IP (e.g 192.168.0.102). In N2, I am forwarding TCP/80 to DVR static IP (e.g. 192.168.1.18). DSL modem/router on N1 has the setting for DynDNS service saved.

On a computer connected to N2, DVR viewable when typing DVD IP (192.168.1.18) address directly, but when using DDNS address, the browser tries to load the router log-in page for Netgear router (N2) but fails.

On computer connected to the ASUS switch in N1, typing the WAN IP (192.168.0.102) of N2 loads the DVR, but typing the DDNS address only successfully loads the DSL modem/router (N1) log-in page.

On a computer connected somewhere on Internet, typing DDNS address fails to load anything after a 20sec wait, during which something seems to be trying to load but ultimately fails.

What am I doing wrong here? I double-checked all the settings to make sure I haven't missed anything. I am not able to change the port of DVR, the only settings inside its control panel are:

1) IP - which I've set to a static one (e.g. 192.168.1.18) 2) Mask - which is N2 router DHCP setting (255.255.255.0) 3) Gateway - which is N2 router DHCP setting (192.168.1.1) 4) Server - not too sure about this so set to 192.168.1.1 as well

Thank you all very much in advance.