Huawei E3531 with Asus router

[pgp]

I own this e3531 modem and I am trying to use it as the modem for my router. Everything is working but it seems the modem does not pass through the external IP, but rather a private IP from it's own range - in fact always 192.168.8.100. If I use a different modem like a D-Link dw157 usb dongle, then I do get the external IP. I refer to the wan ip address in the router. I need the external ip as I am trying to set-up ddns and openvpn.
Question is - how can I get the e3531 to pass the external IP to the router and not change it to a private ip address. Any thoughts will be appreciated.

 

[VANT]

192.168.8.x is a modem own ip. Everythink is ok.

 

[pgp]

192.168.8.x is a modem own ip. Everythink is ok.

Understood, but what I really want is the external IP. I am hoping that you can configure the modem to pass thru the external IP.

 

[VANT]

Your external IP is not 192.168.8.x.
For me my e3372 have 192.168.8.1 IP but external ip is 32.xx.xx.xx. I use dual wan. When i left mouse buton on secondary wan i see external IP.

 

[pgp]

Your external IP is not 192.168.8.x.
For me my e3372 have 192.168.8.1 IP but external ip is 32.xx.xx.xx. I use dual wan. When i left mouse buton on secondary wan i see external IP.

I am using it as primary WAN and not in dual wan mode. I will check on my other set-up to see if dual wan is getting in the way.