Ddclient doesn't check the dns result when it tries to update. It checks its cache file an when value saved in the cache differs from the result it got, it does an update. So if you want to force an update, you could do it this way:
ddclient -use=ip -ip=1.2.3.4 -daemon=0
-use=web | obtain IP from an IP discovery page on the web. This is the default way if none is specified |
-use=if | obtain IP from the -if {interface}. |
-use=ip | obtain IP from -ip {address}. |
-use=cmd | obtain IP from the -cmd {external-command}. |
-use=fw | obtain IP from the firewall specified by -fw {type|address}. |