As far as i know, that model does not have DDNS function.
You can, however, use a client software on your computer to update changes to WAN IP.
I forgot the name of such a client but I'm sure google will turn up an answer.
You will only get the LAN IP and not WAN IP from ipconfig command.
To get WAN IP, just browse around the modem config pages, it should be there.
Or you can go to this page
Current IP Check to get it.
Hope it helps