Difference between localhost and 127.0.0.1 in CI implmentation?

[eluser]Unknown[/eluser]
Hi all,

In my CI server I have configured the following:

$config['base_url'] = 'http://127.0.0.1';

I have written several pages. Now under most circumstances, I can access the webpages normally by using both http://127.0.0.1/welcome and http://localhost/welcome, no problem. However, once I introduce sessions, then the 'localhost' one just does not work. Anyone knows why? Thanks a lot in advance.