Fortigate DDNS problem solved behind AT&T 2Wire 3600HGV router

AT&T U-verse modem/router 2Wire model 3600HGV is unable to set it as bridge mode for any router behind it. Therefore, the Fortigate router with NAT mode and using DHCP option on WAN1 port will always get 192.168.1.### from 3600HGV router, the DDNS with www.dyndns.com will use the 192.168.1.### as its Dynamic IP address which is not right. The DDNS supposed to get a real world IP by using router with bridge mode.
So, here is solution for this issue by using DMZplus setup under the 2Wire router:
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Logon http://192.168.1.254 to the 3600HGV 2Wire router.
Click on TAB: Settings
Click on TAB: Firewall
Click on Application, Pinholes and DMZ
Click on Choose Fortigate Router ID
Select (*)Allow all applications (DMZplus mode) - ..... under 2)Edit firewall settings for this computer.
Click on Save button
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Reboot Fortigate router. The WAN1 port will get a real world IP address which is as same as the IP from the 2Wire 3600HGV router.