Wildcards in reverse DNS

[Paul Colquhoun]

On Tuesday 09 January 2007 04:28, Clenna Lumina wrote:
> > On Sat, Jan 06, 2007 at 11:15:32AM -0800, Clenna Lumina wrote:
> >> Marc Haber wrote:

> > Quoting from Wikipedia:
> >
> > IPv6 addresses are normally written as eight groups of four
> > hexadecimal digits. For example,
> > 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 is a valid IPv6 address.
> >
> > If a four-digit group is 0000, the zeros may be omitted. For
> > example, 
> > 2001:0db8:85a3:0000:1319:8a2e:0370:1337 can be shortened as
> > 2001:0db8:85a3::1319:8a2e:0370:1337. Following this rule, any group 
> > of consecutive 0000 groups may be reduced to two colons, as long as 
> > there is only one double colon used in an address. Leading zeros in 
> > a group can also be omitted. Thus, the addresses below are all valid
> > and equivalent:
> >
> > 2001:0db8:0000:0000:0000:0000:1428:57ab
> > 2001:0db8:0000:0000:0000::1428:57ab
> > 2001:0db8:0:0:0:0:1428:57ab
> > 2001:0db8:0:0::1428:57ab
> > 2001:0db8::1428:57ab
> > 2001:db8::1428:57ab
> 
> Thank you, this helps a lot :)
> 
> > Having more than one double-colon abbreviation in an address is
> > invalid, as it would make the notation ambiguous.
> 
> How so? If such a notation means zero, wouldn't
>    2001:db8:::1428:57ab
> just essentially translate to
>    2001:db8:0000:0000::1428:57ab


The problem with more than one '::' in an IPv6 address happens when they 
are separated.

What is the full version of the following address?

2001:db8::1428::57ab ?

is it      2001:0db8:0000:0000:1248:0000:5718
or is it   2001:0db8:0000:1248:0000:0000:5718 ?


-- 
Reverend Paul Colquhoun, ULC.    http://andor.dropbear.id.au/~paulcol
     Asking for technical help in newsgroups?  Read this first:
        http://catb.org/~esr/faqs/smart-questions.html#intro