Ok I did some test but first I have to set some things straight, the glitch I talk about occurs every 4 seconds, the time pattern is exactly the same. The glitch looks like this: my car (or other cars in spec mode) slightly changes position on track, a glitch to the left or the right, and this every 4 seconds so I'm not able to race like this, very annoying.
I don't get the problem in single player.
As I mentioned above I once plugged the cable directly in the modem but the problem remained, so it's not the HUB.
Trying another cable is not that easy, my pc is far away from the modem (20 metres) so I first have to get another cable or move the pc to the modem for the test. Maybe tomorrow
I don't know what a Z-blocker is.
All un-usefull ports are disabled.
I tried a fresh LFS install in a new folder, the latest version, no luck.
I disabled the windows firewall, no luck in online LFS.
I did the pingtest again and now I don't get the packet loss anymore
I have to make clear that this problem only came with my new system so I'm not currently looking for the ISP to be the cause. I don't have problems playing other games in online modus.