Robtex

Up: 58.87.16.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 58.87.16.0/23
Down right: 58.87.18.0/23

IP	Type	Hostname
58.87.16.0	PTR	user16-0.rcn.ne.jp
58.87.17.2	A+PTR	user17-2.rcn.ne.jp
58.87.18.237	PTR	user18-237.rcn.ne.jp
58.87.19.2	A+PTR	user19-2.rcn.ne.jp
58.87.19.71	A+PTR	user19-71.rcn.ne.jp
58.87.19.86	A+PTR	user19-86.rcn.ne.jp
58.87.19.219	A+PTR	user19-219.rcn.ne.jp