This is multi-threaded tool for doing bulk reverse DNS lookups to locate host names. It handles multiple host names (i.e. multiple host names bound to a single IP). I have released it as a Windows standalone .EXE for simplicity.

The tool returns no output for unsuccessful lookups and is only limited by the speed of your ISP's DNS server. It can happily reverse a class B in around 6 minutes.

rdns 10.0.0.0/24

You can download rDNS from here.