DHCP Server - ip address leases have no host names

Hi Experts

windows 2003 R2 server - dedicated dhcp server

in my address leases everytime i saw a bunch of ip addresses issued without host names

are these ip addresses legitimate can i setup or configure dhcp so it can not issue addresses without a hostname.

can i also prevent dhcp servcies to stop issuing ip addresses to ipods and phones

please advise

thanks

AK