Multiple remote users of ROS master: nickname lookup failure

edit

I am setting up a ROS master that I want students to be able to access, without giving them administrator privileges on that machine. For this example a student laptop has the name vaio4 and has gotten an IP address through the campus wireless network DHCP. The students are able to remotely say

rostopic list

but when they try

rosnode ping gazebo

the master machine prints out an error message about not being able to reach machine vaio4. If I put vaio4 with its current IP address in the /etc/hosts file on the ROS master, everything works. It does not seem that saying

ROS_IP=xxx
or
ROS_HOSTNAME=xxx

on the ROS Master machine makes sense since it is talking to many laptops simultaneously, so which IP address should it use? The laptop knows who it is and can reach the master. It seems that the master should always use numeric IP addresses and not attempt to use machine names or nicknames.

Thanks, Chris