I did some testing and think that I found a working solution with the help of this and this page.
You can create a Web login page and put in the header the following code:
{if $smarty.server.REMOTE_ADDR|substr:0:10 == "192.168.1."}<meta http-equiv="refresh" content="0;url=http://google.com"/>{/if}
{if $smarty.server.REMOTE_ADDR|substr:0:12 == "192.168.251."}<meta http-equiv="refresh" content="0;url=http://microsoft.com"/>{/if}
<meta http-equiv="refresh" content="0;url=http://arubanetworks.com"/>
This will take the client IP ($smarty.server.REMOTE_ADDR) then take the first 10 characters from it (in the case of 192.168.1.10 that will be 192.168.1.) and compare that to a string "192.168.1."; if that matches, a meta refresh will be outputted that redirects the client to a specific URL. In the example that is Google, in practice you will put the URL of your guest page for the 192.168.1.x subnet. Similar all clients in 192.168.251.x will go to microsoft.com (or your second guest page). If none matches, it will redirect to arubanetworks.com.
For testing, you can put in the code block for example:
{$smarty.server.REMOTE_ADDR}<br>
{$smarty.server.REMOTE_ADDR|substr:0:16}<br>
{'192.168.1.10'|substr:0:10}<br>
{'192.168.251.32'|substr:0:12}<br>
to get the client IP, then the client IP truncated at 10 characters, and then an example address truncated at 10 characters and one truncated at 12 characters.
You can clean the footer/login message if you like.
Would this solve your request?