Very easy but VERY cool to use:
For an index.php that will be installed on many servers that are installed in a web without DNS, the page should point to the server itself and, for example for a cups-webinterface to port 631. So, lets do it:
<a href="/testdir/">testlink</a><br>
<a href="http://<? echo apache_getenv("SERVER_ADDR"); ?>:631/">Cups Webinterface</a><br>
Have a lot of fun . . .
Hela