Robtex

Up: 5.61.12.0/23
Can't show all results, try to descend to a more specific CIDR
Down left: 5.61.13.0/25
Down right: 5.61.13.128/25
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
5.61.13.0	PTR	spb.avantel.ru
5.61.13.51	PTR	email.sibselmash.ru
5.61.13.52	PTR	mx.onegroup.ru
5.61.13.52	A	mx.churique.ru
5.61.13.52	A	mail.churique.ru
5.61.13.58	PTR	ip-5-61-13-58.spb.avantel.ru
5.61.13.58	A	mail.gismap3d.ru
5.61.13.58	A	gismap3d.ru
5.61.13.59	A+PTR	mail.itain.spb.ru
5.61.13.59	A	ithelpspb.ru
5.61.13.59	A	mail.infokosmo.ru
5.61.13.61	PTR	mail.vmsi.ru
5.61.13.68	PTR	ip-5-61-13-68.spb.avantel.ru
5.61.13.68	A	pm-office.net
5.61.13.69	PTR	ip-5-61-13-69.spb.avantel.ru
5.61.13.69	A	tm-office.net
5.61.13.83	A+PTR	rumx.tpvaoc.com
5.61.13.110	A+PTR	ip-5-61-13-110.spb.avantel.ru
5.61.13.110	A	mail.pge.ru
5.61.13.116	A+PTR	milestone.ivosystems.ru
5.61.13.118	PTR	mail.happyoffice.pro
5.61.13.118	PTR	happyoffice.pro
5.61.13.118	PTR	post.aplusdevelopment.ru
5.61.13.122	A+PTR	mail.nevamt.spb.ru
5.61.13.162	A+PTR	sslvpn.happyoffice.pro
5.61.13.164	PTR	milestone.ivosystems.ru
5.61.13.165	A+PTR	ipsecvpn.happyoffice.pro
5.61.13.166	PTR	happyoffice.pro
5.61.13.167	PTR	mail.happyoffice.pro
5.61.13.169	A+PTR	1cweb.happyoffice.pro
5.61.13.170	A+PTR	remote.aplus.spb.ru
5.61.13.171	A+PTR	ip-5-61-13-171.spb.avantel.ru
5.61.13.171	A	mail2.happyoffice.pro
5.61.13.196	A+PTR	ip-5-61-13-196.spb.avantel.ru
5.61.13.201	A+PTR	ip-5-61-13-201.spb.avantel.ru
5.61.13.240	PTR	ip-5-61-13-240.spb.avantel.ru
5.61.13.255	PTR	ip-5-61-13-255.spb.avantel.ru