Matching IPv6 address to a CIDR subnet

Question

Is there a good way to match an IPv6 address to an IPv6 subnet using CIDR notation? What I am looking for is the IPv6 equivalent to this: Matching an IP to a CIDR mask in PH

Answer 1

PHP can perform bitwise operations on strings!

• IPv4 or IPv6
• No base conversion
• No ASCII bit strings
• Pretty fast

<?php

/**
 * Does the given IP match the CIDR prefix?
 */
function matchIp(string $ip, string $cidr): bool
{
  // Get mask bits
  list($net, $maskBits) = explode('/', $cidr);

  // Size
  $size = (strpos($ip, ':') === false) ? 4 : 16;

  // Convert to binary
  $ip = inet_pton($ip);
  $net = inet_pton($net);
  if (!$ip || !$net) {
    throw new InvalidArgumentException('Invalid IP address');
  }

  // Build mask
  $solid = floor($maskBits / 8);
  $solidBits = $solid * 8;
  $mask = str_repeat(chr(255), $solid);
  for ($i = $solidBits; $i < $maskBits; $i += 8) {
    $bits = max(0, min(8, $maskBits - $i));
    $mask .= chr((pow(2, $bits) - 1) << (8 - $bits));
  }
  $mask = str_pad($mask, $size, chr(0));

  // Compare the mask
  return ($ip & $mask) === ($net & $mask);
}

Answer 2

Basically http://www.phpclasses.org/browse/file/70429.html

To use it, simply call

$cidr = new CIDR();
$cidr->match($ipv6, $ipv6_in_cidr);

Result is 'Good'.

Answer 3

Since you cannot convert IPv6 addresses to integer, you should operate bits, like this:

$ip='21DA:00D3:0000:2F3B:02AC:00FF:FE28:9C5A';
$cidrnet='21DA:00D3:0000:2F3B::/64';

// converts inet_pton output to string with bits
function inet_to_bits($inet) 
{
   $splitted = str_split($inet);
   $binaryip = '';
   foreach ($splitted as $char) {
             $binaryip .= str_pad(decbin(ord($char)), 8, '0', STR_PAD_LEFT);
   }
   return $binaryip;
}    

$ip = inet_pton($ip);
$binaryip=inet_to_bits($ip);

list($net,$maskbits)=explode('/',$cidrnet);
$net=inet_pton($net);
$binarynet=inet_to_bits($net);

$ip_net_bits=substr($binaryip,0,$maskbits);
$net_bits   =substr($binarynet,0,$maskbits);

if($ip_net_bits!==$net_bits) echo 'Not in subnet';
else echo 'In subnet';

Also, if you use some database to store IPs, it may already have all the functions to compare them. For example, Postgres has an inet type and can determine, whether IP is contained within subnet like this:

SELECT 
   '21DA:00D3:0000:2F3B:02AC:00FF:FE28:9C5A'::inet << 
   '21DA:00D3:0000:2F3B::/64'::inet;

9.11. Network Address Functions and Operators in PostgreSQL

Answer 4

If your masks are always divisible by four (which is quite common in ipv6). You can use:

function checkIPv6WithinRange($ipv6, $range) {
    list ($net, $mask) = preg_split("/\//", $range);

    if ($mask % 4)
        throw new NotImplementedException("Only masks divisible by 4 are supported");
    $stripChars = (128-$mask)/4;

    $hexNet = bin2hex(inet_pton($net));
    $reducedNet = substr($hexNet, 0, 0 - $stripChars);

    $hexIp = bin2hex(inet_pton($ipv6));
    $reducedIp = substr($hexIp, 0, 0 - $stripChars);

    return $reducedIp === $reducedNet;
}

Answer 5

Here is an example that works by checking an IP address against a list of individual IPs or CIDRs, both IPv4 and IPv6:

https://gist.github.com/lyquix-owner/2620da22d927c99d57555530aab3279b

<?php
// IP to check
$ip_check = $_SERVER['REMOTE_ADDR'];

// Array of allowed IPs and subnets, both IPv4 and IPv6
$ips_allowed = array(
    '192.30.252.0/22'
    '2620:112:3000::/44'
    '192.168.16.104'
);

// Flag for IP match allowed list
$ip_match = false;

foreach($ips_allowed as $ip_allow) {
    // If IP has / means CIDR notation
    if(strpos($ip_allow, '/') === false) {
        // Check Single IP
        if(inet_pton($ip_check) == inet_pton($ip_allow)) {
            $allow = true;
            break;
        }
    }
    else {
        // Check IP range
        list($subnet, $bits) = explode('/', $ip_allow);

        // Convert subnet to binary string of $bits length
        $subnet = unpack('H*', inet_pton($subnet)); // Subnet in Hex
        foreach($subnet as $i => $h) $subnet[$i] = base_convert($h, 16, 2); // Array of Binary
        $subnet = substr(implode('', $subnet), 0, $bits); // Subnet in Binary, only network bits

        // Convert remote IP to binary string of $bits length
        $ip = unpack('H*', inet_pton($ip_check)); // IP in Hex
        foreach($ip as $i => $h) $ip[$i] = base_convert($h, 16, 2); // Array of Binary
        $ip = substr(implode('', $ip), 0, $bits); // IP in Binary, only network bits

        // Check network bits match
        if($subnet == $ip) {
            $allow = true;
            break;
        }
    }
}
if(!$allow) {
    die('IP not allowed');
}

Answer 6

I created my own solution, using the following code:

function iPv6MaskToByteArray($subnetMask) {
  $addr = str_repeat("f", $subnetMask / 4);
  switch ($subnetMask % 4) {
    case 0:
      break;
    case 1:
      $addr .= "8";
      break;
    case 2:
      $addr .= "c";
      break;
    case 3:
      $addr .= "e";
      break;
  }
  $addr = str_pad($addr, 32, '0');
  $addr = pack("H*" , $addr);
  return $addr;
}

function iPv6CidrMatch($address, $subnetAddress, $subnetMask) {
  $binMask = iPv6MaskToByteArray($subnetMask);
  return ($address & $binMask) == $subnetAddress;
}

Note that $address and $subnetAddress were obtained by running the string address through inet_pton. Call the function as follows:

$subnet = inet_pton("2001:06b8::");
$mask = 32;
$addr = inet_pton("2001:06b8:0000:0000:0000:0000:1428:07ab");
$match = iPv6CidrMatch($addr, $subnet, $mask); // TRUE