PHP5 calculate IPv6 range from cidr prefix?

Question

I am able to do this with IPv4 using code snippets from various online sources. I was wondering if there was a way to do it with IPv6.

Basically I just need a form that I can enter an IPv6 address and prefix (ex: f080:42d2:581a::0/68) and it calculates the network address, first useable address, last useable address, and broadcast address. Then just prints to screen. Not looking to store it in a database or anything yet.

Answer 1

First of all: IPv6 doesn't have network and broadcast addresses. You can use all addresses in a prefix. Second: On a LAN the prefix length is always (well, 99.x% of the time) a /64. Routing a /68 would break IPv6 features like stateless auto configuration.

Below is a verbose implementation of an IPv6 prefix calculator:

<?php

/*
 * This is definitely not the fastest way to do it!
 */

// An example prefix
$prefix = '2001:db8:abc:1400::/54';

// Split in address and prefix length
list($firstaddrstr, $prefixlen) = explode('/', $prefix);

// Parse the address into a binary string
$firstaddrbin = inet_pton($firstaddrstr);

// Convert the binary string to a string with hexadecimal characters
# unpack() can be replaced with bin2hex()
# unpack() is used for symmetry with pack() below
$firstaddrhex = reset(unpack('H*', $firstaddrbin));

// Overwriting first address string to make sure notation is optimal
$firstaddrstr = inet_ntop($firstaddrbin);

// Calculate the number of 'flexible' bits
$flexbits = 128 - $prefixlen;

// Build the hexadecimal string of the last address
$lastaddrhex = $firstaddrhex;

// We start at the end of the string (which is always 32 characters long)
$pos = 31;
while ($flexbits > 0) {
  // Get the character at this position
  $orig = substr($lastaddrhex, $pos, 1);

  // Convert it to an integer
  $origval = hexdec($orig);

  // OR it with (2^flexbits)-1, with flexbits limited to 4 at a time
  $newval = $origval | (pow(2, min(4, $flexbits)) - 1);

  // Convert it back to a hexadecimal character
  $new = dechex($newval);

  // And put that character back in the string
  $lastaddrhex = substr_replace($lastaddrhex, $new, $pos, 1);

  // We processed one nibble, move to previous position
  $flexbits -= 4;
  $pos -= 1;
}

// Convert the hexadecimal string to a binary string
# Using pack() here
# Newer PHP version can use hex2bin()
$lastaddrbin = pack('H*', $lastaddrhex);

// And create an IPv6 address from the binary string
$lastaddrstr = inet_ntop($lastaddrbin);

// Report to user
echo "Prefix: $prefix\n";
echo "First: $firstaddrstr\n";
echo "Last: $lastaddrstr\n";

?>

It should output:

Prefix: 2001:db8:abc:1400::/54
First: 2001:db8:abc:1400::
Last: 2001:db8:abc:17ff:ffff:ffff:ffff:ffff

Answer 2

For those who stumble upon this question, you can do this more effectively using the dtr_pton and dtr_ntop functions and dTRIP class found on GitHub.

We also have noticed a lack of focus and tools with IPv6 in PHP, and put together this article, http://www.highonphp.com/5-tips-for-working-with-ipv6-in-php, which may be of help to others.

Function Source

This converts and IP to a binary representation:

/**
 * dtr_pton
 *
 * Converts a printable IP into an unpacked binary string
 *
 * @author Mike Mackintosh - [email protected]
 * @param string $ip
 * @return string $bin
 */
function dtr_pton( $ip ){

    if(filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)){
        return current( unpack( "A4", inet_pton( $ip ) ) );
    }
    elseif(filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)){
        return current( unpack( "A16", inet_pton( $ip ) ) );
    }

    throw new \Exception("Please supply a valid IPv4 or IPv6 address");

    return false;
}

This converts a binary representation to printable IP:

/**
 * dtr_ntop
 *
 * Converts an unpacked binary string into a printable IP
 *
 * @author Mike Mackintosh - [email protected]
 * @param string $str
 * @return string $ip
 */
function dtr_ntop( $str ){
    if( strlen( $str ) == 16 OR strlen( $str ) == 4 ){
        return inet_ntop( pack( "A".strlen( $str ) , $str ) );
    }

    throw new \Exception( "Please provide a 4 or 16 byte string" );

    return false;
}

Examples

Using the dtr_pton function you can:

$ip = dtr_pton("fe80:1:2:3:a:bad:1dea:dad");
$mask = dtr_pton("ffff:ffff:ffff:ffff:ffff:fff0::");

Get your Network and Broadcast:

var_dump( dtr_ntop( $ip & $mask ) );
var_dump( dtr_ntop( $ip | ~ $mask ) );

And your output would be:

string(18) "fe80:1:2:3:a:ba0::"
string(26) "fe80:1:2:3:a:baf:ffff:ffff"