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

[Dave Rynne]

> 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,

Ermmm - isn't the 2002 bit hardcoded in the code above ? So how can it
be wrong ?

2002:7f00:0001:0:0:0:0:0 (or even 2002:7f00:1::) looks fine to me.


> and secondly the 0001
> I think can have the 0 droped from it. Is this correct?

Indeed it can be compressed to '1' - same way as in IPv4 '127.000.000.001'
gets compressed down to '127.0.0.1'

> 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?

No.

Also - you can replace the trailing '0:0:0:0:0' with '::'

Or you could you install ipv6calc and use it:
dave at freyja:~$ ipv6calc --ipv4_to_6to4addr 127.0.0.1
2002:7f00:1::

Dave

>
> 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
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