I am helping to organize a little conference. There is no internet connection, so we are limited to a mobile LTE connection with a limited volume.
We have a Ubuntu-based server that acts as a router, provides a DHCP and DNS server and routes from its subnet 192.168.1.0/24 to the LTE connection (USB Stick).
Even though our configuration of NATing from the internal network to the LTE-based internet works, we want to prevent that a client uses too much of the valuable volume, and limit each client (MAC address?) to a certain amount of data, e.g. 100MB. If a client reaches that limit (sum of up- and downloads), we want to be informed (a log entry suffices), and he should be either throttled (if possible) or cut off from the internet connection (but he should still be able to communicate in the local network).
Is there any mechanism or software we could use for this scenario?