Robtex

Up: 188.172.128.0/20
Can't show all results, try to descend to a more specific CIDR
Down left: 188.172.136.0/22
Down right: 188.172.140.0/22
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
188.172.136.144	PTR	188-172-136-144.ctelnetco.com
188.172.137.1	A+PTR	outbyoip1.pod17.euw1.zdsys.com
188.172.137.1	A	mail.pod-7.int.zendesk.com
188.172.137.1	A	in.vip.pod7.fra1.zdsys.com
188.172.137.2	PTR	188-172-137-2.ctelnetco.com
188.172.137.3	A+PTR	outbyoip3.pod17.euw1.zdsys.com
188.172.137.8	A+PTR	outbyoip8.pod17.euw1.zdsys.com
188.172.137.32	A	vap.vip.fra1.zdsys.com
188.172.137.68	A	out1.pod7.fra1.zdsys.com
188.172.137.71	A	out4.pod7.fra1.zdsys.com
188.172.137.86	A	deferred3.pod7.fra1.zdsys.com
188.172.137.100	A	out1.pod11.fra1.zdsys.com
188.172.137.101	A	out2.pod11.fra1.zdsys.com
188.172.137.103	A	out4.pod11.fra1.zdsys.com
188.172.138.1	PTR	outbyoip1.pod18.euc1.zdsys.com
188.172.138.1	A	bootstrappedventures.zendesk.com
188.172.138.1	A	bridgeclublive.zendesk.com
188.172.138.3	PTR	188-172-138-3.ctelnetco.com
188.172.138.8	A	outbyoip8.pod18.euc1.zdsys.com
188.172.138.9	PTR	188-172-138-9.ctelnetco.com
188.172.138.9	A	p7.zdusercontent.com
188.172.138.9	A	zdusercontent.vip.pod7.fra1.zdsys.com
188.172.138.65	PTR	188-172-138-65.ctelnetco.com
188.172.138.66	PTR	188-172-138-66.ctelnetco.com
188.172.138.66	A	tradeshift.ssl.zendesk.com
188.172.138.74	PTR	188-172-138-74.ctelnetco.com
188.172.138.74	A	support.hostway.com
188.172.138.82	PTR	188-172-138-82.ctelnetco.com
188.172.138.95	A	autocom.ssl.zendesk.com
188.172.138.98	PTR	188-172-138-98.ctelnetco.com
188.172.138.98	A	strava.ssl.zendesk.com
188.172.138.98	A	support.strava.com
188.172.138.129	PTR	188-172-138-129.ctelnetco.com
188.172.138.129	A	cdkeys.ssl.zendesk.com
188.172.138.129	A	support.cdkeys.com
188.172.138.130	A	cerberusllc.ssl.zendesk.com
188.172.138.130	A	support.cerberusftp.com
188.172.138.131	PTR	188-172-138-131.ctelnetco.com
188.172.138.156	A	jbsupsource.ssl.zendesk.com
188.172.138.156	A	youtrack-support.jetbrains.com
188.172.138.156	A	hub.ssl.zendesk.com
188.172.140.1	PTR	proxy.vip.pod11.fra1.zdsys.com
188.172.140.1	A	jdwilliams-uk.zendesk.com
188.172.140.1	A	bookingsecurity.zendesk.com
188.172.140.2	PTR	188-172-140-2.ctelnetco.com