Question: So recently i gave my friend a URL on facebook chat while we were discussing on how much further we have to go on a booking system, my friend says he cant open the link, when i tried clicking it worked but what caught my eye was the referring URL by facebook: 

> 
> <https://www.facebook.com/>**l.php**?u=https%3A%2F%2F192.168.42.149%2FIS314%2Freservations.php
> 
> 
> 

I was intrigued by the l.php (L.PHP), what actually does l.php do? I googled and a author speculated something on privacy at this page <http://www.codehesive.com/index.php/archive/facebook-privacy-and-the-mystery-of-l-php/> but nothing too certain. So i was wondering if anyone has a clear idea of what l.php could be, i find this interesting (weird i know). Thanks!

Answer: 
No one can know what exactly that script does but the developers at Facebook.

I presume they track all outgoing links from Facebook to get some statistics on them and on the users. After that it just sends you to the external page.
Please check out the following article [Facebook, privacy and the mystery of l.php](http://web.archive.org/web/20160826060705/http://www.codehesive.com:80/index.php/archive/facebook-privacy-and-the-mystery-of-l-php/) which says:

> 
> Unless it’s from a public page, all you’re bound to see is one simple
>  referring URL: <http://www.facebook.com/l.php>. Facebook ‘wraps’ all
>  links on Facebook within this simple file — once you click on a link
>  in Facebook, l.php will ‘redirect’ you to the actual URL. Why Facebook
>  does this is unclear.
> 
> 
> 

So now you have more questions to answer.

Update: Sorry, I just realised that you posted actually the same link.