Robtex

Up: 66.47.16.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 66.47.20.0/23
Down right: 66.47.22.0/23

IP	Type	Hostname
66.47.20.102	A	user-112u536.biz.mindspring.com
66.47.20.192	PTR	user-112u560.biz.mindspring.com
66.47.20.236	A	user-112u57c.biz.mindspring.com
66.47.21.2	PTR	user-112u582.biz.mindspring.com
66.47.21.52	A	user-112u59k.biz.mindspring.com
66.47.22.136	A	user-112u5k8.biz.mindspring.com
66.47.23.83	PTR	mail.securiport.com
66.47.23.85	PTR	user-112u5ql.biz.mindspring.com
66.47.23.85	A	securiport.net