How to know which version of the Internet Protocol (IP) a client is using when connecting to my server?

Question

I want to check via php if someone connects to my site via IPv4 or IPv6.

The client address can be found in $_SERVER[\"REMOTE_ADDR\"] but

Answer 1

You can use this:

function ipVersion($txt) {
     return strpos($txt, ":") === false ? 4 : 6;
}

Answer 2

What about counting the number of '.' and/or ':' in $_SERVER["REMOTE_ADDR"] ?

If there is more than 0 ':', and no '.' symbol in $_SERVER["REMOTE_ADDR"], I suppose you can consider you user is connected via IPv6.

Another solution might be to use the filter extension : there are constants (see the end of the page) that seem to be related to IPv4 and IPv6 :

FILTER_FLAG_IPV4 (integer)
Allow only IPv4 address in "validate_ip" filter.

FILTER_FLAG_IPV6 (integer)
Allow only IPv6 address in "validate_ip" filter.

Answer 3

You can use AF_INET6 to detect if PHP is compiled with IPv6 support:

<?php
if ( defined('AF_INET6') ) {
    echo 'Yes';
} else {
    echo 'No';
}
?>

Answer 4

You can use inet_pton:

<?php

$packedIp = @inet_pton($ip);

if ($packedIp === false) {
    // invalid IP
} else if (isset($packedIp[4])) {
    // IPv6
} else {
    // IPv4
}

Answer 5

IPv4 addresses all match the regex /^\d{1,3}(\.\d{1,3}){3,3}$/.

Answer 6

Check for IPv4

$ip = "255.255.255.255";
if(filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {    
    echo "Valid IPv4";
}
else {
    echo "Invalid IPv4";
}

Check for IPv6

$ip = "FE80:0000:0000:0000:0202:B3FF:FE1E:8329";    
if(filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
    echo "Valid IPv6";
}
else {
    echo "Invalid IPv6";
}

For more, check PHP function filter_vars and list of filters for validation.