A DNS reconnaissance tool for locating non-contiguous IP space
Fierce is a semi-lightweight scanner that helps locate
non-contiguous IP space and hostnames against specified
domains. It's really meant as a pre-cursor to nmap,
unicornscan, nessus, nikto, etc, since all of those
require that you already know what IP space you are
looking for. This does not perform exploitation and
does not scan the whole internet indiscriminately. It
is meant specifically to locate likely targets both
inside and outside a corporate network. Because it uses
DNS primarily you will often find mis-configured networks
that leak internal address space. That's especially useful
in targeted malware.