[ILUG] [OT] - One for the IPv6 guys

[AJ McKee]

Hi All,

I am trying to figure out this IPv6 stuff here, especially in a script
I need to generate IPv6 addresses from a list of IPv4 addresses in a
database. But I am not too sure if I am on the right road or not. Dave
Wilson gave a good presentation on IPv6 at an AGM a few years ago, but
I cannot see to find it... maybe its gone.

Anyhow, here is a wee function in php to calculate the IPv6 address,
modified from one I found on hotscripts;

function ipv4Toipv6 ($ipv4Address) {
	if(!$ipv4Address) {
		return false;
	}
	list($octet1, $octet2, $octet3, $octet4) = split ("\.", $ipv4Address, 4);
	$decimal = ((((($octet1 * 256 + $octet2) *256 ) + $octet3) * 256 ) + $octet4);
	$hex = dechex($decimal);
	$splitHex = str_split($hex, 4);
	$ipv6 = "2002:$splitHex[0]:$splitHex[1]:0:0:0:0:0";
	return $ipv6;
}
echo ipv4Toipv6("127.0.0.1");

This produces;


2002:7f00:0001:0:0:0:0:0

Which is wrong, firstly the 2002 should be FFFF, and secondly the 0001
I think can have the 0 droped from it. Is this correct? I can work
around the FFFF or the reserved addresses issues, however if I left
the preceding 0's in would that invaildate any address I enter?

If I run my home IP address through this (212.17.57.169) I get
2002:d411:39a9:0:0:0:0:0 which appears to be correct.

So, I am almost there I think, but alas my understanding of IPv6 is
very limited, if anyone can point out a few pitfalls of the above way
and things I need to consider that would be great.

Thanks In advance.
AJ