Robtex

Up: 192.5.68.0/23
Can't show all results, try to descend to a more specific CIDR
Down left: 192.5.68.0/25
Down right: 192.5.68.128/25
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
192.5.68.20	A+PTR	ns2.clearfunds.com
192.5.68.20	A+PTR	ns2.level1events.com
192.5.68.20	PTR	ns2.rivalsystems.com
192.5.68.36	A+PTR	spam06.clearfunds.com
192.5.68.36	A+PTR	spam06.level1events.com
192.5.68.36	A+PTR	spam06.rivalsystems.com