[ Thanks to Falko
Timme for this link. ]
“This article shows how you can configure a Debian Etch system
that has the webhosting control panel ISPConfig installed so that
ISPConfig can be accessed on port 80. By default ISPConfig uses
port 81 which is a non-standard port and is blocked by some
firewalls and ISPs. By using Apache’s mod_proxy module, we can
avoid this problem. It lets us create a reverse proxy that can
fetch the pages from ISPConfig on port 81…”