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/