Robtex

Up: 204.141.56.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 204.141.56.0/23
Down right: 204.141.58.0/23
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
204.141.56.2	PTR	ademco.com
204.141.56.2	A	honeywellsecuritygroup.com
204.141.56.4	PTR	wwwnotes.ademco.com
204.141.56.4	PTR	internet1.ademco.com
204.141.56.4	PTR	pop.ademco.com
204.141.56.6	PTR	stream1.ademco.com
204.141.56.6	A+PTR	mail3.alarmnet.com
204.141.56.32	PTR	pittway.com
204.141.56.34	PTR	firstalertpro.com
204.141.56.35	A+PTR	xetron.pittway.com
204.141.56.44	A+PTR	alarmnet.com
204.141.56.44	A	alarmnet-me.com
204.141.56.47	A	firstalertprofessional.biz
204.141.56.47	A	firstalertprofessional.info
204.141.56.75	A+PTR	video.alarmnet.com
204.141.56.80	A+PTR	services.alarmnet.com
204.141.56.85	A	www.totalconnect.net
204.141.56.85	A	totalconnect.net
204.141.56.100	A	auiproxy1.alarmnet.com
204.141.56.101	A+PTR	auiproxy1b.alarmnet.com
204.141.56.119	A+PTR	mail.alarmnet.com
204.141.56.124	A	alarmnetdirect.com
204.141.56.140	A+PTR	symphonytest.alarmnet.com
204.141.56.143	A	dealertest.aui.alarmnet.com
204.141.56.145	A	alarmnet360.com
204.141.56.152	A+PTR	mail2.alarmnet.com
204.141.56.180	A	rs.alarmnet.com
204.141.56.185	A	totalconnect2.com
204.141.56.250	A	f1.alarmnet.com
204.141.56.251	A	v1.alarmnet.com
204.141.57.1	PTR	dnsb1.ademco.com
204.141.57.10	PTR	dnsb10.ademco.com
204.141.57.31	PTR	dnsb31.ademco.com
204.141.57.100	A+PTR	auiredir1.alarmnet.com
204.141.57.101	A+PTR	auiredir2.alarmnet.com
204.141.58.80	A+PTR	dataserver1.alarmnet.com
204.141.58.81	A+PTR	dataserver2.alarmnet.com
204.141.58.115	PTR	dnsc115.ademco.com
204.141.58.115	A	controlserver.alarmnet.com