Fierce is not an IP scanner or not a DDOS tool also its not designed to scan the whole internet or perform any UN-targeted attacks.
It is supposed specifically to locate likely targets both inside and out outside a company network. Only those targets are listed (unless the -no pattern switch is used). No exploitation is performed (unless you are doing something intentionally malicious with the -connect switch). Fierce may be a reconnaissance tool. Fierce may be a PERL script that quickly scans domains (usually in only a couple of minutes, assuming no network lag) using several tactics.
1)sudo apt-get install fierce
2) fierce -dns www.test.com