DDNSNotify logs into a (telnet-enabled) router and retrieves the WAN IP Address, only IF the IP Address differs from the DNS IP address for the domain name. It's useful to update DNS records using another external DDNS script (such as zoneclient.py).
Dynamically update your network's external IP address to a host name service such as DHS International (dhs.org) or DynDNS.org (dyndns.org) so that you can access your network using a host name. Even works behind routers such as Linksys and Netgear.