Am I correct in remembering that you have an APU system. If yes, then that system is not capable of running at the full bandwidth with IPS running.
If I am remembering wrong, please provide info on which system you do have IPFire on.
I used to have the APU4 mini system and that maxed out at around 200MBit with the IPS running while my line capability was 1GBit.
I now have the new mini appliance and that runs at around 1GBit with the IPS enabled.
Because I was interested in real time performance, I did the tests against a speedtest server in the internet.
My results show commisioned speed with iperf3. This speed was measured by a Vodafone technician at my router (Fritz!Box), also.
@flinx , welcome to the community.
And thanks for your advice. But this wasn’t/isn’t the problem. Internet is bridged to LAN2 and this interface runs at 1000MBit.