I'm not sure, but I think DDNS is supposed to update on wanup, however mine doesnt seem to update.
Can someone tell me how to fix it, or failing a script to put into my wanup
Since it works for me, and apparently for many others, the problem must be on your end.
Make sure the router's time is properly updated from NTP server. Erase the nvram ("thorough" option) and reconfigure manually if the problem persists.