Robtex

Up: 81.17.0.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 81.17.4.0/23
Down right: 81.17.6.0/23
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
81.17.4.6	A+PTR	mail3.nscekb.ru
81.17.4.10	PTR	uralsbank.ru
81.17.4.54	A+PTR	chumail.sestry.ru
81.17.4.54	A	churoute.sestri.ru
81.17.4.54	A	chumail.sestri.ru
81.17.4.61	PTR	61.4.17.81.ekb.enforta.com
81.17.4.66	PTR	kfgateway.slad.ru
81.17.4.66	A	kf2.slad.ru
81.17.4.70	PTR	mail.bella-ural.ru
81.17.4.70	A	mail2.bella-ural.ru
81.17.4.85	PTR	85.4.17.81.ekb.enforta.com
81.17.4.86	A	prom.nexcom.ru
81.17.4.90	A+PTR	fulcrum.nexcom.ru
81.17.4.98	PTR	mail.generation.ru
81.17.4.98	A	download.inkoopbeleid2017.zilverenkruis.nl
81.17.4.103	PTR	103.4.17.81.ekb.enforta.com
81.17.4.134	A+PTR	vektorv.nexcom.ru
81.17.4.137	PTR	137.4.17.81.ekb.enforta.com
81.17.4.138	A+PTR	sve-su.nexcom.ru
81.17.4.141	PTR	141.4.17.81.ekb.enforta.com
81.17.4.142	A	mail.fatfactory.ru
81.17.4.142	A	router.fatfactory.ru
81.17.4.142	A	relay1.fatfactory.ru
81.17.4.156	PTR	156.4.17.81.ekb.enforta.com
81.17.4.162	A	bangbonsomer.nexcom.ru
81.17.4.194	PTR	2by2.ru
81.17.4.196	PTR	196.4.17.81.ekb.enforta.com
81.17.4.206	PTR	relay.tkrem.ru
81.17.4.207	PTR	207.4.17.81.ekb.enforta.com
81.17.4.214	PTR	214.4.17.81.ekb.enforta.com
81.17.4.218	PTR	218.4.17.81.ekb.enforta.com
81.17.4.222	A+PTR	sergio2.nexcom.ru
81.17.4.246	A+PTR	yodlik.nexcom.ru
81.17.4.251	PTR	251.4.17.81.ekb.enforta.com
81.17.5.6	PTR	6.5.17.81.ekb.enforta.com
81.17.5.6	A	jaha.biz
81.17.5.30	PTR	energo.pssr.ru
81.17.5.30	A	energo.nexcom.ru
81.17.5.54	PTR	iko.ru
81.17.5.70	PTR	mail.uraltermosvar.ru
81.17.5.90	A+PTR	wolf.nexcom.ru
81.17.5.110	A+PTR	smpz.nexcom.ru
81.17.5.126	A+PTR	csc.nexcom.ru
81.17.5.182	A+PTR	school.nexcom.ru
81.17.5.254	A	etme.nexcom.ru
81.17.6.0	PTR	0.6.17.81.ekb.enforta.com
81.17.6.6	A+PTR	edc.nexcom.ru
81.17.6.54	A	mail2.bmiko.ru
81.17.6.117	PTR	mail.uralairlines.ru
81.17.6.119	PTR	ironmail.uralairlines.ru
81.17.6.188	PTR	188.6.17.81.ekb.enforta.com
81.17.6.255	PTR	255.6.17.81.ekb.enforta.com
81.17.7.0	PTR	0.7.17.81.ekb.enforta.com
81.17.7.10	PTR	zheldore.ru
81.17.7.22	PTR	mail.akrond.ru
81.17.7.26	PTR	mail.vitamotors.ru
81.17.7.255	PTR	255.7.17.81.ekb.enforta.com