Robtex

Up: 192.40.160.0/20
Can't show all results, try to descend to a more specific CIDR
Down left: 192.40.168.0/22
Down right: 192.40.172.0/22

IP	Type	Hostname
192.40.168.6	A	mailer6.gate168.rs.smtp.com
192.40.168.160	A+PTR	mailer160.gate168.rs.smtp.com
192.40.169.1	A	mailer1.gate169.rs.smtp.com
192.40.169.7	A	mailer7.gate169.rs.smtp.com
192.40.169.8	A	mailer8.gate169.rs.smtp.com
192.40.169.10	A+PTR	mailer10.gate169.rs.smtp.com
192.40.169.11	A	mailer11.gate169.rs.smtp.com
192.40.169.38	A	mailer38.gate169.rs.smtp.com
192.40.170.2	A+PTR	mailer2.gate170.rs.smtp.com
192.40.170.4	A	mailer4.gate170.rs.smtp.com
192.40.170.20	A	mailer20.gate170.rs.smtp.com
192.40.170.27	A	mailer27.gate170.rs.smtp.com
192.40.172.18	PTR	18-172.rs.smtp.com
192.40.172.42	A	mailer42.gate172.rs.smtp.com
192.40.172.58	PTR	58-172.rs.smtp.com
192.40.173.1	PTR	mailer1.gate173.rs.smtp.com
192.40.173.14	A	mailer14.gate173.rs.smtp.com
192.40.173.19	A+PTR	mailer19.gate173.rs.smtp.com
192.40.173.117	A	mailer117.gate173.rs.smtp.com
192.40.173.118	A	mailer118.gate173.rs.smtp.com
192.40.173.131	A	mailer131.gate173.rs.smtp.com
192.40.173.142	A	mailer142.gate173.rs.smtp.com
192.40.173.143	A	mailer143.gate173.rs.smtp.com
192.40.173.191	A	mailer191.gate173.rs.smtp.com
192.40.173.213	A	mailer213.gate173.rs.smtp.com
192.40.173.229	A	mailer229.gate173.rs.smtp.com
192.40.175.19	A+PTR	mailer19.gate175.rs.smtp.com
192.40.175.75	A+PTR	mailer75.gate175.rs.smtp.com
192.40.175.122	A+PTR	mailer122.gate175.rs.smtp.com
192.40.175.145	A+PTR	mailer145.gate175.rs.smtp.com
192.40.175.202	A+PTR	mailer202.gate175.rs.smtp.com
192.40.175.217	A+PTR	mailer217.gate175.rs.smtp.com