Robtex

Up: 27.123.40.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 27.123.44.0/23
Down right: 27.123.46.0/23

IP	Type	Hostname
27.123.44.51	PTR	unknown-27-123-44-x.yahoo.com
27.123.44.161	PTR	unknown-27-123-44-x.yahoo.com
27.123.44.204	PTR	unknown-27-123-44-x.yahoo.com
27.123.44.215	PTR	unknown-27-123-44-x.yahoo.com
27.123.45.65	PTR	unknown-27-123-45-x.yahoo.com
27.123.45.144	PTR	unknown-27-123-45-x.yahoo.com
27.123.45.221	PTR	unknown-27-123-45-x.yahoo.com
27.123.46.5	PTR	unknown-27-123-46-x.yahoo.com
27.123.46.100	PTR	unknown-27-123-46-x.yahoo.com