Ranges for Dynamic IP Addresses

Hello, 

I am attempting to set some security on an Internet app.  Basically that all requests originating from IP addresses outside of a set range will not be able to execute admin actions.

I know Xfinity's  IP addresses are dynamic, thus will change.  But is there a range or ranges that I can use in that security setting that would cover Comcast?  

It is looking for information in this format:

'allowed_admin_ranges' => ['127.0.0.1/8','192.168.0.0/16','fd00::/8',],

When looking at my Xfinity IP assignment, I see 10.0.0.123/24.  Would that be the range?

Thanks in advance!