@Virgo 

I get the point to test independent from the ISP.  Nevertheless the speedtest gives me the expected speed if I don't pass via the ER7212-router.  

Will test using the iperf program when I get the change when I get home.

 ok, finaly found the time to do some more tests.

These are the results with iPerf:

Connecting to host 192.168.2.30, port 5201
[  4] local 192.168.100.15 port 61935 connected to 192.168.2.30 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  35.4 MBytes   296 Mbits/sec
[  4]   1.00-2.00   sec  35.1 MBytes   295 Mbits/sec
[  4]   2.00-3.00   sec  35.2 MBytes   295 Mbits/sec
[  4]   3.00-4.00   sec  35.1 MBytes   295 Mbits/sec
[  4]   4.00-5.00   sec  32.5 MBytes   272 Mbits/sec
[  4]   5.00-6.00   sec  35.1 MBytes   295 Mbits/sec
[  4]   6.00-7.00   sec  35.1 MBytes   295 Mbits/sec
[  4]   7.00-8.00   sec  35.1 MBytes   294 Mbits/sec
[  4]   8.00-9.00   sec  35.2 MBytes   296 Mbits/sec
[  4]   9.00-10.00  sec  34.9 MBytes   293 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.00  sec   349 MBytes   293 Mbits/sec                  sender
[  4]   0.00-10.00  sec   349 MBytes   293 Mbits/sec                  receiver

They are a lot more then the 100 Mbps that I received from my ISP but according to the specs from the ER7212 I should see some other numbers:

Then I have put my laptop directly on the bridge the ISP is providing me, so not passing the router from the ISP.  This is to test if I could get different results on the bridging mode from the modem but unfortunately I'm getting a normal result.  

  @crrodriguez , wel I did change the IP-address of the WAN-port to 192.168.2.3 and put a PC on that port to make the iperf-test, as it is described here: iperf

So I didn't just test the switch but also the router capabilities.

But you guys were right.  I completed rewired the entire house and there was a old cable I must have missed.  Alltough it linked at 1 Gbps it didn't deliver the linked speed and that of course did confuse me.  

This is the speed I get now: Not to far from the 300 Mbps subscription I have.

  @Mr.Blue Great, that's within the expected speed margins of DOCSIS 3ish provider..ensure you got current firmware on the modem too..those who are still in support have gotten improvements in the SQM stuff since covid.

And yeah, cables sting sometimes.. network cards are very smart and will negotiate highest speed possbile even if the cable is wacky.. of course you wont achieve the required throughtput.

  @crrodriguez , thank you for your advice in any way. Unfortunately we don't have free choice of modem here in Belgium (yet) so the provider won't let people interfere with modemfirmware whatsoever. It took them more then 4 weeks to make it possible to have the modem setup in bridge mode. Spent hours on their helpdesk just to get it fixed. But now that all my bad cables are gone and my setup is finally in bridge mode I hope that I can start enjoying this setup for many years.