[TYPO3-english] reverse proxy on same server with same address

[dev at stean.ch]

Hello everybody,

I have typo3, version 4.6.1, introductionpackage installed.

There are 2 apache servers running, one on port 81, internal
server, and the other one on port 80, external and proxy.

I an new with typo3, tried to set reverseProxyIP, or, proxy_host,
whatever I did, typo3 tries to access the server with port 81
instead of 80.

For the moment, the only thing that makes my instance work is
playing around with the file t3lib/class.t3lib_div.php

where the following line decides that proxy and server may not
be the same:

if (self::cmpIP($_SERVER['REMOTE_ADDR'],  
$GLOBALS['TYPO3_CONF_VARS']['SYS']['reverseProxyIP'])) {

So my question is, what am I doing wrong in the typo3 configuration,
how can I tell typo3 to build URL's with port 80 instead of 81.

Thanks for the help,

Stephan