The IP address field is populated by looking that the router ARP caches for each subnet. If you are using a PIX, FWSM, or ASA as your router, then you will not see IP addresses in UT unless you are using UTLite or Dynamic User Tracking with DHCP snooping. Your routers must be supported by Campus Manager, and must appear as green with router (or layer 3 switch) icons on the topology map.

Once UT has found the IP addresses, then it will look them up in DNS or the server's local hosts file to get the hostnames.