On Mon, Apr 18, 2011 at 04:26:12PM +0200, Raimo Niskanen wrote:
> On Mon, Apr 18, 2011 at 12:10:31PM +0200, Alessandro Baggi wrote:
> > Hi list. I'm making a program that maps some ip address to a specified
> > dns. My problem is relative to CNAME record.
> :
> > Supposing that I have 209.85.148.104 ip, is possible (only knowing the
> > ip) go back to the CNAME record www.google.it?
>
> It is as far as I know impossible.
>
> A PTR record points to the canonical name.
>
> One host can have several IP addresses but every IP address
> can hence only have one canonical name.
>
> A CNAME record is supposed to resolve to a canonical name,
> but often enough there is one or more extra indirections
> before you reach it.
>
> There can be CNAME records in any domain so you can not find all
> resolving to a given canonical name unless searching the _whole_ DNS.
Yes, DNS doesn't (need or) support this. I'm pretty sure that there are
some databases of IP -> name mappings, though, presumably compiled by
finding valid hostnames and looking up their IPs.
Joachim
--
PotD: net/transmission,-qt - lightweight BitTorrent client with Qt interface
http://www.joachimschipper.nl/
