DDclient is a small but full featured Perl client used to update 
dynamic DNS entries for accounts on Dynamic DNS Network Services 
free DNS service. It has the capability to update more than only 
dyndns and it can fetch your WAN-ipaddress on a few different ways.

Supported features include: operating as a daemon, manual and 
automatic updates, static and dynamic updates, optimized updates for
multiple addresses, MX, wildcards, abuse avoidance, retrying failed 
updates, and sending update status to syslog and through e-mail.
