3G / UMTS traffic limit/ bandwidth monitor

[basti <black.fledermaus@arcor.de>]

Hello,

I have a 3G / UMTS Stick and I want to use my Linuxbox (Raspbbery) as a
router to share that UMTS connection to multiple devices.

That works so far.

Now I want to Monitor the traffic.

For example

device 1 = 2GB traffic limit
device 2 = 1GB traffic limit
device 3 = 500 MB traffic limit

How can I monitor the traffic on my raspi and disable the internet
connection for a device that reach there limit?

I found vnstat but it seems that is is monitor only...


Best Regards,
Basti