Hi, I have not enabled the uPnP plugin and didn't put any rule for NAT on my router, as i had to do on another computer on my LAN, in other port. Interestingly, everything works (i thought that it shouldn't, can someone make that clear for me, why it works nonetheless?), though a few minutes after i open Ktorrent i can't browse the web, but any current download that i have in Firefox for example, continues without trouble. After those few minutes, everything goes back to normal.

I use debian testing with Ktorrent 4.3.1

In regards to not having the port forwarded - it is still possible for torrents to work without this, however performance may be degraded and it will be more difficult for you to seed to others (which may in turn limit your download speeds depending on how other clients are configured).

As for why you have issues browsing the web - please ensure KTorrent isn't saturating your internet connection by comparing the download speeds when you are affected by this issue, and when you are not.