Here's a piece off code as example:

<?php
echo "Your Ip Addres is " . $_SERVER['REMOTE_ADDR'] ."<br/>";
if ( $_SERVER['HTTP_VIA'] ) {
    echo "Your are using proxy server " . $_SERVER['HTTP_VIA'] ."<br />";
} else {
    echo "No VIA header detected";
}
//echo $_SERVER['HTTP_VIA'];
if ( $_SERVER['HTTP_X_FORWARDED_FOR'] ) {
    echo "Your are proxied and the proxied address is " . $_SERVER['HTTP_X_FORWARDED_FOR'] ."<br />";
} else {
    echo "No Forward address detected";
}
?>

// Denied IP's.
    $deny_ips = array(
        '127.0.0.1',
        '192.168.100.1',
        '192.168.200.1',
        '192.168.300.1',
        'xxx.xxx.xxx.xxx'
    );
 
    // $deny_ips = file('blocked_ips.txt');
 
    // read user ip adress:
    $ip = isset($_SERVER['REMOTE_ADDR']) ? trim($_SERVER['REMOTE_ADDR']) : '';
 
    // search current IP in $deny_ips array
    if (($i = array_search($ip, $deny_ips)) !== FALSE){
 
        // $i = contains the array key of the IP adress.        
 
        // user is blocked:
        print "Your IP adress ('$ip') was blocked!";
        exit;
    }
 
    // If we reach this section, the IP adress is valid