You need to know the MAC address of the switch, or , at least the MAC prefix (The first three octets of a six-octet ethernet address uniquely identifies the hardware vendor - This is called the "Organizationally Unique Identifier" (OUI)) of the manufacturer.

You can look this up for your vendor at http://standards.ieee.org/db/oui/index.html.

If you have access to your DHCP server, you should be able to match this MAC prefix or address with the list of DHCP-distributed addresses, and determine the IP address.

If you do not have access to DHCP, but are on the same unrouted subnet as the switch, you can ping the entire subnet range, then look at your arp table, then find the mac for the Infiniband switch, and trace back to the IP.