IP Address of the machine in PHP gives ::1 but why?

::1 is the actual IP. It is an ipv6 loopback address (i.e. localhost). If you were using ipv4 it would be 127.0.0.1.

If you want to get a different IP address, then you'll need to connect to the server through a different network interface.

If you are trying to run localhost, this answer will fix your problem. Just few changes on

apache2/httpd.conf 

search all "listen" words ex:

Listen 80

Make like this.

Listen 127.0.0.1:80

than restart your apache

$_SERVER[REMOTE_ADDR]

will show Listen 127.0.0.1

you can see answer in this detailed answer link

If you mean getting the user's IP address, you can do something like :

<?php
    if(!empty($_SERVER['HTTP_CLIENT_IP'])){
      $ip=$_SERVER['HTTP_CLIENT_IP'];
    }
    elseif(!empty($_SERVER['HTTP_X_FORWARDED_FOR'])){
      $ip=$_SERVER['HTTP_X_FORWARDED_FOR'];
    }
    else{
      $ip=$_SERVER['REMOTE_ADDR'];
    }
?>

<?php echo  "<br />".$ip;?>

It will get the user's actual IP address, regardless of proxies etc.

$_SERVER['REMOTE_ADDR'] is the IP address of the client.

$_SERVER['SERVER_ADDR'] is the IP address of the server.

Reference: http://php.net/manual/en/reserved.variables.server.php