I have been suffering from a lame internet connection, since we got the new provider and the Fritz!Box. I just couldn't really determine, what is the culprit for it being so slow - despite raising speed from 1000 to 3000 kBit/s.
When I some time ago found out, that my flatsharer with his Windoze XP machine, doesn't suffer from performance reduction (that dumbass - why couldn't he tell me that before?!? He knew, that I had problems!!), the only question remaining to me, was:
What cool technology do I use with Linux, that he doesn't on XP?
Well, the answer is simple - IPv6 !
After recompiling my kernel to have IPv6 support as a module and not loading that - weeee, do I have some fast internet! :)
This also explains, why it was much faster with the former setup - using a SuSE 9.1 machine for routing. The Linux-machine knows, how to handle IPv6 - Fritz!Box doesn't... :-/
Let's hope, that they will fix this!