This is how to update the dynamic assigned IP of a single host, where the domain is registered on ENOM.COM registrar.

Here we simply setup a contab chunk on a debian/ubuntu installation. Probably it is the same syntax on others distro. We only need the wget command with some arguments.

...
# updating a dynamic IP versus ENOM.COM. Run every 15 minutes, forever.
# m   h  dom  mon  dow  user  command
*/15  *  *    *    *    root  wget -q --delete-after "http://dynamic.name-services.com/interface.asp?command=setdnshost&zone=example.com&domainpassword=secret&hostname=www"
...