HowtoMatrix

This article shows how you can do port-forwarding with rinetd
on Debian Etch. rinetd allows you to forward ports from one system to
another. This useful if you have moved your web sites to a new server
with a different IP address. Of course, you have modified your DNS
records, but it can take a few days until DNS changes become effective,
and that is where rinetd comes into play. If clients still use the old
DNS records, rinetd can redirect them to the new server. With rinetd,
you do not have to fiddle with iptables rules.

Read more at HowtoForge