Free host address registration on DynDNS expires after 30 days if you
have not re-registered your IP in that amount of time.  A typical
broadband IP address does not change that often so dynamic DNS client
does not try to register the IP address.  Please include an option to
register the WAN IP address with DynDNS (or dynamic IP address service
of choice) every X number of days regardless the last time the address
changed.

Thanks.