Robtex

Up: 173.31.40.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 173.31.40.0/23
Down right: 173.31.42.0/23

IP	Type	Hostname
173.31.40.248	A	173-31-40-248.client.mchsi.com
173.31.41.167	PTR	173-31-41-167.client.mchsi.com
173.31.42.23	A	173-31-42-23.client.mchsi.com
173.31.42.48	A	173-31-42-48.client.mchsi.com
173.31.42.51	A+PTR	173-31-42-51.client.mchsi.com
173.31.42.219	A+PTR	173-31-42-219.client.mchsi.com