php/ipv6wildcard.php

   1 #!/usr/bin/php
   2 <?php
   3
   4 /**
   5  * (c) 2020 - Tomas Mudrunka <harvie@github>
   6  *
   7  * Given IPv6 address and prefix creates array of * wildcard suffixed
   8  * addresses to be used for as reverse DNS records
   9  */
  10 function ipv6_prefix2wildcards($address, $prefix) {
  11         //Special case of /0 prefix
  12         if($prefix == 0) return ['*'];
  13
  14         //Parse ip and prefix
  15         echo("IPv6 prefix: ".$address."/".$prefix."\n");
  16         $addr = inet_pton ($address);
  17         $pref = $prefix;
  18         $a = gmp_import($addr);
  19
  20         //Separate maskable octets
  21         $pref_hex = ceil($pref / 4); //Number of prefix octets
  22         $pref_bin = $pref_hex*4; //Number of prefix octets in bits
  23         $pref_rem = $pref_bin - $pref; //Remainder of prefix
  24         echo("Rounding prefix: ".$pref_bin."-".$pref_rem."\n");
  25
  26         $a = gmp_div_q($a, gmp_pow(2,128-$prefix)); //Truncate to just prefix
  27         $a = gmp_mul($a, gmp_pow(2,$pref_rem)); //Fill remaining bits in last wildcard octet with zeros
  28
  29         //Generate wildcards
  30         $wildcards = [];
  31         for($i = 0; $i < (2**$pref_rem) ; $i++) {
  32                 //echo("ADDED: ".$i." = ".decbin($i)."\n");
  33                 $ap = gmp_or($a, gmp_init($i));
  34                 $w = gmp_strval($ap, 16);
  35                 $w = str_repeat('0', $pref_hex-strlen($w)).$w;
  36                 if(strlen($w) < 32) $w.='*';
  37                 $wildcards[] = $w;
  38         }
  39
  40         return $wildcards;
  41 }
  42
  43 function ipv6_string2rev($str) {
  44         return implode('.',str_split(strrev($str)));
  45 }
  46
  47 if(isset($argv[2])) {
  48         $wcs = ipv6_prefix2wildcards($argv[1],$argv[2]);
  49 } else {
  50         $wcs = ipv6_prefix2wildcards('2001:1:3::10', 67);
  51 }
  52
  53 echo("\n");
  54 foreach($wcs as $w) {
  55         echo($w."\n");
  56 }
  57
  58 echo("\n");
  59 foreach($wcs as $w) {
  60         echo(ipv6_string2rev($w)."\n");
  61 }