calculate IP range using PHP and CIDR

Question

I\'ve seen various questions and answers around this site and I\'m still having difficulty wrapping my head around this problem (could be because I\'ve got a cold). Regardle

Answer 1

I created this php function in order to get the subnet splits of a network/range. It works with ipv4 or ipv6.
If php<5.4 then use this hex2bin function https://github.com/dompdf/dompdf/issues/1692

function divide_ip_range($cidr="2001:db8:abc:12ff::/54",$mindivs=2){ // input range 192.168.4.0/24 and returns array with the 1st range and 2nd range [0] => 192.168.4.0/25 , [1] => 192.168.4.127/25
  $outarr=array();
  list($ipaddr,$range) = explode('/', $cidr);
  for($rngsplit=1;pow(2,$rngsplit)<$mindivs;$rngsplit++){} // find to how many networks to divide
  $divs=pow(2,$rngsplit);    
  $divcidr=(int)$range+$rngsplit;
  if(preg_match("/^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$/",$ipaddr)){ // IPv4
    $ip_address_long = ip2long($ipaddr);
    $ip_nmask_long=(-1 << (32 - $range));
    $ip_net = $ip_address_long & $ip_nmask_long;
    $ip_broadcast_invert = ~$ip_nmask_long;
    $ip_last = ($ip_address_long | $ip_broadcast_invert) - 1;
    $ip_broadcast = $ip_address_long | $ip_broadcast_invert;
    $numofhosts=pow(2,32-$range)-2;
    for ($i=0;$i<$divs;$i++){
      $outarr[]=long2ip($ip_net+$i*ceil($numofhosts/$divs)+($i*ceil($numofhosts/$divs)%2) )."/$divcidr";
    }
    //echo "Net:$ipaddr/$range\nFirst:".long2ip($ip_net)."\nLast: ".long2ip($ip_last)."\nNumOfHosts:$numofhosts \n";
  } else if (preg_match("/^[0-9a-f:]+$/",$ipaddr)) { // IPv6 section 
    $ip_addr_bin = inet_pton($ipaddr);
    $ip_addr_hex = bin2hex($ip_addr_bin);
    $flexbits = 128 - $range; // Calculate the number of 'flexible' bits for first net
    $pos = 31; $addr_hex_first = $ip_addr_hex; $addr_hex_last = $ip_addr_hex;
    while ($flexbits > 0) {
      $orig_val = hexdec(substr($ip_addr_hex, $pos, 1)); // dec value of pos char. ex. f=15
      $mask = 0xf << (min(4,$flexbits)); // calculate the subnet mask. min() prevents comparison to be negative 
      $new_val_first = $orig_val & $mask;
      $addr_hex_first = substr_replace($addr_hex_first, dechex($new_val_first) , $pos, 1); // Put hex character in pos
      $segmask=(pow(2,min(4,$flexbits))-1); // Last address: OR it with (2^flexbits)-1, with flexbits limited to 4 at a time
      $new_val_last = $orig_val | $segmask;
      $addr_hex_last = substr_replace($addr_hex_last, dechex($new_val_last) , $pos, 1);
      $pos--; $flexbits -= 4; // Next nibble
    }
    $partpos=(4*floor($pos/4)); // The 4 digits that vary by the subnetting
    $partfirst=substr($addr_hex_first,$partpos,4);
    $partlast=substr($addr_hex_last,$partpos,4);
    $numofhosts=(hexdec($partlast)+1-hexdec($partfirst));
    for ($i=0;$i<$divs;$i++){
      $partdiv=dechex(hexdec($partfirst)+$i*$numofhosts/$divs);
      $addr_hex_div=substr_replace($addr_hex_first, $partdiv , $partpos, 4);
      $outarr[]=inet_ntop(hex2bin($addr_hex_div))."/$divcidr";
    }  
    //echo "Net:$ipaddr/$range\nFirst:".inet_ntop(hex2bin($addr_hex_first))."\nLast:".inet_ntop(hex2bin($addr_hex_last))."\nNumOfHosts:$numofhosts\nDivide at partpos:$partpos ($partlast+1-$partfirst)/$divs=$partdiv\n";
  }
  return $outarr;
}