I wrote the following nsupdate-ddns.sh script to update the dynamic DNS entry for my laptop when switching network locations. There are several ways to execute a script like this automatically (cronjob, startup script, launcher, etc.) — I chose to use Sidekick for Mac OS X, which allows me to execute it when switching locations (either network or physical). This script can also create the private authentication key needed by the DDNS BIND server, and will display some sample configuration values. If you’re setting up a new DDNS BIND server, you can use the examples to configure your dynamic zone file.