The problem comes probably from your modem. I suppose your internet cable goes first in the modem and then from the modem to your router and from there to your computer? In this case, you will have to forward the traffic from your modem first to your router and from your router to your computer.

And: no, this is not of little significance, since it will prevent you from downloading faster than ~60% of the max speed (and many downloads will not start at all)...

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</td><td><a href="http://crawler.trillinux.org"><img align="right" style="border:0" src="http://crawler.trillinux.org/img/netsize.png" alt="Network size"></a></td></table>