How to calculate the next ipv6 address? - php

Question

I've got stuck on a hopefully simple task: I want to get the next ip address.
Here are some of my tests:
//$binaryIp = inet_pton('192.168.1.1');
$binaryIp = inet_pton('2001:cdba::1');
$verySimple = inet_ntop(
$binaryIp++
);
var_dump($verySimple); //'2001:cdba::1'
$simpleMaths = inet_ntop(
$binaryIp + inet_pton('0.0.0.1')
);
var_dump($simpleMaths); //inet_ntop(): Invalid in_addr value
$aLittleBitOfSuccess = long2ip(
ip2long(inet_ntop($binaryIp)) + 1
);
var_dump($aLittleBitOfSuccess); //'0.0.0.1' but with IPv4 '192.168.1.2'
OK, until here it's obvious that my tries are more nonsense than a real aproach to my problem but what else can I try? I've searched the web and found some solutions for subnet calculations and stuff like that but nothing for simple addition or subtraction.
My next try would be to split the string from inet_ntop() and fiddle around with the hex-values but there must be a simple solution to add 1 to an in6_addr!

Answer 1

With a few exceptions, an IPv6 address is divided into two 64-bit parts: the Network/Subnet and the Interface ID. You should be interested in the 64 bits of the Interface ID.
The easiest thing to do is to parse the address into the two 64-bit unsigned integers, increment the Interface ID, then recombine the two parts into a 128-bit address.

Answer 2

I've choosen the hex-way and made this function:
protected function binaryIncrement($binaryIp, $increment = 1) {
//inet_pton creates values where each "character" is one ip-address-byte
//we are splitting the string so we can handle every byte for itselve.
$binaryIpArrayIn = str_split($binaryIp);
$binaryIpArrayOut = array();
$carry = 0 + $increment;
//reverse array because our following addition is done from right to left.
foreach (array_reverse($binaryIpArrayIn) as $binaryByte) {
//transforming on byte from our ip address to decimal
$decIp = hexdec(bin2hex($binaryByte));
$tempValue = $decIp + $carry;
$tempValueHex = dechex($tempValue);
//check if we have to deal with a carry
if (strlen($tempValueHex) > 2) {
//split $tempValueHex in carry and result
//str_pad because hex2bin only accepts even character counts
$carryHex = str_pad(substr($tempValueHex,0,1),2,'0',STR_PAD_LEFT);
$tempResultHex = str_pad(substr($tempValueHex,1,2),2,'0',STR_PAD_LEFT);
$carry = hexdec($carryHex);
} else {
$carry = 0;
$tempResultHex = str_pad($tempValueHex,2,'0',STR_PAD_LEFT);
}
//fill our result array
$binaryIpArrayOut[] = hex2bin($tempResultHex);
}
//we have to reverse our arry back to normal order and building a string
$binaryIpOut = implode(array_reverse($binaryIpArrayOut));
return $binaryIpOut;
}
$binaryIpV6In = inet_pton('2001:cdba::FFFF');
$binaryIpV6Out = $this->binaryIncrement($binaryIpV6In);
var_dump(inet_ntop($binaryIpV6Out));
$binaryIpV4In = inet_pton('192.168.1.1');
$binaryIpV4Out = $this->binaryIncrement($binaryIpV4In, 256);
var_dump(inet_ntop($binaryIpV4Out));
This way I can use the same method for IPv4 and IPv6.