How to make a page to know Ipv6?

Question

To know Ipv4 I can use the code on a page:

<?php
    echo $_SERVER["REMOTE_ADDR"];
?>

But I can not find anything similar to do the same with Ipv6, what I get a lot is already sites with converters.

Even if there is no code like the above for Ipv6, I would like to be able to make one that fixes the conversion automatically to Ipv6.

And the end result was for example 2002:55F6:9A82:0:0:0:0:0 as can be seen in link

Answer 1

What defines the address is the connection

The variable $_SERVER["REMOTE_ADDR"]; shows both Ipv4 and Ipv6. It only depends on how the server network is configured, and how the client accessed their page.

If the machine is serving an address via Ipv4 you will get something like:

208.67.222.222

if you are serving for Ipv6, you will already have something on that line:

2001:0db8:85a3:08d3:1319:8a2e:0370:7344

Edit in response to a comment: if you already have a server that serves Ipv6, just force the Ipv6 request to your server to see the REMOTE_ADDR working in practice. For example, putting Ipv6 in the href of some link, or in the URL of a iframe or requisition ajax if you prefer. Nothing prevents you from testing both Ipv4 and Ipv6 on the same page, but for this you need to make both requests separately.

To standardize the storage

PHP has the function inet_pton(), which understands both forms, and converts the address to a binary compact version.

Just to illustrate, I made a small function that converts any valid IP into Ipv6 long:

<?php
   function normalizeIP( $ip ) {
      $ip = inet_pton( $ip );
      if( strlen( $ip ) < 5 ) {
         $ip = chr( 255 ).chr( 255 ).str_pad( $ip, 4, chr( 0 ), STR_PAD_LEFT );
      }
      $ip = str_split( str_pad( $ip, 16, chr( 0 ), STR_PAD_LEFT ) );
      $out = '';
      for( $i = 0; $i < 16; ) {
         if( $i && $i % 2 == 0 ) $out .= ':';
         $out .= str_pad( dechex( ord( $ip[$i++] ) ), 2, '0', STR_PAD_LEFT );
      }
      return $out;
   }
?>

See on IDEONE.

Of course in practice you probably won’t need any of this, just store the result of inet_pton() in a field that accepts binary strings of variable size up to 16 characters.

In short

This depends only on the configuration of the server connection, and even if the machine meets both protocols, it may happen to the client A be using Ipv4, and a customer B by Ipv6. Both will have their respective IP stored in $_SERVER["REMOTE_ADDR"].

If you have both protocols enabled on the server, may be that Ipv4 is converted to an Ipv6 notation and you get these results (note the prefix ::ffff indicating that it is an Ipv4 in Ipv6 format):

::ffff:192.000.002.124
::ffff:192.0.2.124
0000:0000:0000:0000:0000:ffff:c000:027c
::ffff:c000:027c
::ffff:c000:27c

All addresses above are equivalent to Ipv4 192.0.2.124.