Limiting internet access

Hi,

my router is currently connected to the internet via both a surfstick (all the time, limited traffic per month) and my phone (only sometimes, unlimited volume).

All I do at the moment is to set the route metric in such a way that when both my surfstick and the phone are available the traffic is routed via the phone.

I would now like to take some precaution so that the limited data volume of the surfstick is not accidentally depleted by some data-hungry application so I would like to limit the internet access via the surfstick either by throttling the available bandwidth or by limiting the amount of data a device can use per day.

So all traffic that originates on the router should not be limited in any way, all traffic that originates from a client device should be limited when the surfstick is used, however low amounts of data are fine, I would not want to completely cut off the clients.

Is something like this possible with openwrt and how would I go about it?

Many thanks!

With Mwan3 and using ipset rule you can redirect hungry destinations via the unlimited plan connection. E g. youtube, aliexpress, instagram, fb, etc.