Robtex

Up: 203.172.80.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 203.172.80.0/23
Down right: 203.172.82.0/23
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
203.172.80.0	PTR	reverse-203-172-80-0.csloxinfo.net
203.172.80.1	PTR	reverse-203-172-80-1.csloxinfo.net
203.172.80.1	A	pop.bangkokshuho.com
203.172.80.1	A	webmail.eplus.co.th
203.172.80.2	PTR	axmail12.csloxinfo.com
203.172.80.3	PTR	axmail13.csloxinfo.com
203.172.80.4	PTR	axmail14.csloxinfo.com
203.172.80.4	A	mail.janintertrade.com
203.172.80.4	A	webmail.vmi.co.th
203.172.80.5	PTR	axmail15.csloxinfo.com
203.172.80.6	PTR	axmail16.csloxinfo.com
203.172.80.7	PTR	axmail17.csloxinfo.com
203.172.80.8	A+PTR	axmail18.csloxinfo.com
203.172.80.9	A+PTR	axmail19.csloxinfo.com
203.172.80.9	A	mail2.ilct.co.th
203.172.80.9	A	mail.ilct.co.th
203.172.80.84	PTR	reverse-203-172-80-84.csloxinfo.net
203.172.80.134	PTR	reverse-203-172-80-134.csloxinfo.net
203.172.80.155	PTR	reverse-203-172-80-155.csloxinfo.net
203.172.80.173	PTR	reverse-203-172-80-173.csloxinfo.net
203.172.80.219	PTR	reverse-203-172-80-219.csloxinfo.net
203.172.80.255	PTR	reverse-203-172-80-255.csloxinfo.net
203.172.81.0	PTR	reverse-203-172-81-0.csloxinfo.net
203.172.81.17	PTR	reverse-203-172-81-17.csloxinfo.net
203.172.81.48	PTR	reverse-203-172-81-48.csloxinfo.net
203.172.81.141	PTR	reverse-203-172-81-141.csloxinfo.net
203.172.81.210	PTR	reverse-203-172-81-210.csloxinfo.net
203.172.81.223	PTR	reverse-203-172-81-223.csloxinfo.net
203.172.81.224	PTR	reverse-203-172-81-224.csloxinfo.net
203.172.83.37	PTR	reverse-203-172-83-37.csloxinfo.net