Robtex

Up: 206.15.0.0/18
Can't show all results, try to descend to a more specific CIDR
Down left: 206.15.0.0/20
Down right: 206.15.16.0/20

IP	Type	Hostname
206.15.0.0	PTR	unknown.level3.net
206.15.1.1	PTR	dialup-206.15.1.1.dial1.sanfrancisco1.level3.net
206.15.2.2	PTR	dialup-206.15.2.2.dial1.sanfrancisco1.level3.net
206.15.3.129	PTR	dialup-206.15.3.129.dial1.sanfrancisco1.level3.net
206.15.4.22	A	sierraclub.bbnplanet.net
206.15.4.22	A	multilink1.sierraclub.bbnplanet.net
206.15.4.134	A	mto2.bbnplanet.net