Robtex

Up: 27.123.200.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 27.123.204.0/23
Down right: 27.123.206.0/23
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
27.123.204.60	A+PTR	mg31a.mail.vip.tw1.yahoo.com
27.123.204.239	A+PTR	sendmailws110.mail.tw1.yahoo.com
27.123.204.240	PTR	f753.mail.vip.tw1.yahoo.com
27.123.204.240	A	imap-nokia.mail.global.gm0.yahoodns.net
27.123.205.0	PTR	unknown-27-123-205-x.yahoo.com
27.123.205.77	PTR	unknown-27-123-205-x.yahoo.com
27.123.205.77	A	imap4.mail.tw.gm0.yahoodns.net
27.123.205.77	A	imap4-rr.mail.global.gm0.yahoodns.net
27.123.205.79	A	imap-star.mail.tw.gm0.yahoodns.net
27.123.206.31	A	imap-star.mail.tw.gm0.yahoodns.net
27.123.206.55	A+PTR	mta-v1.mail.vip.tw1.yahoo.com
27.123.206.59	A	omp1004.mail.tw1.yahoo.com
27.123.206.62	A	tw56294.ostk.bm2.prod.tw1.yahoo.com
27.123.206.84	A	n5.bullet.mail.tw1.yahoo.com
27.123.206.119	PTR	unknown.yahoo.com
27.123.206.119	A	htc.imap.mail.yahoo.com
27.123.206.119	A	imap10.mail.vip.tw1.yahoo.com
27.123.206.123	PTR	unknown-27-123-206-x.yahoo.com
27.123.206.123	A	htc.imap.mail.yahoo.com
27.123.206.123	A	imap-ssl.mail.yahoo.com
27.123.206.126	A+PTR	pop.mail.vip.tw1.yahoo.com
27.123.206.144	A	mta1016.mail.tw1.yahoo.com
27.123.206.180	A+PTR	mta1052.mail.tw1.yahoo.com
27.123.206.201	PTR	imap12.mail.vip.tw1.yahoo.com
27.123.206.201	A	htc.imap.mail.yahoo.com
27.123.206.201	A	imap-ssl.mail.yahoo.com
27.123.206.229	A	n4-vm2.bullet.mail.tw1.yahoo.com
27.123.207.1	A+PTR	n11-vm1.bullet.mail.tw1.yahoo.com
27.123.207.46	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.55	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.69	PTR	imap13.mail.vip.tw1.yahoo.com
27.123.207.69	A	htc.imap.mail.yahoo.com
27.123.207.69	A	imap-ssl.mail.yahoo.com
27.123.207.70	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.78	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.86	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.93	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.95	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.116	A+PTR	n10-vm8.bullet.mail.tw1.yahoo.com
27.123.207.127	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.135	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.149	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.149	A	htc.imap.mail.yahoo.com
27.123.207.149	A	imap-ssl.mail.yahoo.com
27.123.207.150	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.157	A+PTR	imap15.mail.vip.tw1.yahoo.com
27.123.207.157	A	htc.imap.mail.yahoo.com
27.123.207.157	A	imap-ssl.mail.yahoo.com
27.123.207.159	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.165	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.165	A	htc.imap.mail.yahoo.com
27.123.207.165	A	imap-ssl.mail.yahoo.com
27.123.207.166	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.173	PTR	imap17.mail.vip.tw1.yahoo.com
27.123.207.173	A	htc.imap.mail.yahoo.com
27.123.207.173	A	imap-ssl.mail.yahoo.com
27.123.207.175	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.189	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.199	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.215	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.217	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.223	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.233	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.234	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.235	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.242	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.245	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.247	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.248	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.251	PTR	unknown-27-123-207-x.yahoo.com
27.123.207.255	PTR	unknown-27-123-207-x.yahoo.com