Install Kana Solutions dyndns-updater version 3.1.0.7 or higher which can be found here:

 

http://www.kanasolution.com/products/dyndns-updater/dyndns-download/

 

Once installed, go to the installation folder (usually found in c:\program files (x86)) and edit the DynDNS.ini file.

under [Options] in the ini file, add the following line and save:

UseLanIP=1

 

Restart the dyndns updater application and then when you perform an update, the application will use your local LAN IP instead of your WAN IP.