This requires iOS9 or iOS10.
How to connect 2 or more iPads using a .local address.
To set up WIFI only with a local URL do the following:
In the iPad settings app for the server iPad, name your device with a simple name like: myipadproserver
This is found in settings->General->About->Name
Please use all lower case in the name and no apostrophe.
Next, in the Settings->Network of each unrealBook slave, type in http://myipadproserver.local:8080/
for the address of the server.
Make sure every iPad is connected to the same WiFi network.
That's it. Now the master can change IP and it doesn't matter. The slave will always find the master based on the local address.
The beauty is that you can use an tethered iPhone as a router using Personal Hotspot.
One more note. If your iPad name has spaces like: my awesome ipad
then the address would be: http://my-awesome-ipad.local:8080/
Put the "-" dash instead of the spaces.
NOTE: I have heard that the apostrophe should not be used within the iPad server name. So please remove all apostrophe when naming your server iPad.