one short question

Kevin Darcy kcd at daimlerchrysler.com
Sat Jun 2 00:49:24 UTC 2001


Brad Knowles wrote:

> At 4:20 PM -0400 6/1/01, Kevin Darcy wrote:
>
> >  Nah, the IPv4 address space is only 2^32, so just do a reverse lookup of
> >  every possible address and extract the RDATAs which happen to be in the
> >  desired domain.
>
>         Actually, IPv4 space is smaller than this.  You can ignore Class
> D (224.* and above), the RFC 1918 address spaces, and you should be
> able to get a list of what IP address spaces have not yet been
> assigned, and therefore don't need to be searched.
>
>         However, this won't tell you all the CNAMEs, nor will it tell you
> all the alternative names that are directly resolved into A records
> themselves (but which may not be the canonical name for the
> machine/interface).
>
>         And then there is the issue of IPv6 -- some people are already
> using it, so if you're going to start sweeping all IP space through
> reverse lookups, you'd also have to consider IPv6 as well.

Well, my post was mostly in jest, but just for record, the original poster
did, after all, specifically ask how to get all of the A records in a zone
(thereby rendering irrelevant CNAMEs and IPv6 address records). Multiple
A records can point to the same address, true, but my (facetious) assumption
was that every A record had a corresponding PTR record: this implies that in
such multiple-reference situations, the reverse name would own multiple
PTR records (although most applications and/or resolver implementations would
only see the first one in the list). As for RFC 1918 or not-yet-assigned
ranges, I don't think we can rule those out, since the poster didn't specify
that this was an Internet zone -- internally folks might use RFC 1918
addresses and/or addresses from not-yet-assigned ranges. I think you're right
about Class D, though...


- Kevin




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