IP filtering is disabled by default.
To configure it, I added the following elements in dclib.cfg (usually in ~/.dc directory):
Code:
<ipfilter checktimeout="60">
  <ipfile>/tmp/iplist-1.txt</ipfile>
  <ipfile>/tmp/iplist-2.txt</ipfile>
</ipfilter>

Where:

      checktimeout is the timeout in seconds, after which filters are reloaded if needed. To disable filter: set this value to 0.
      ipfile is a file having some addresses to filter. Each line of this file should have this format: "description: fromip-toip". Entries found in those files are then filtered by valknut. Both upload and download will be disabled.


To conclude, there is no graphical interface to configure this part, and I won't developp such a thing.
Of course, I guess that people interested in the subject already knows where to find black lists... Go there otherwise: http://www.bluetack.co.uk/index.php

3. Implementation
I put the check of IP addresses in CDownloadManager::CheckWaitTransfer(). But maybe that would be better to do this as soon as possible, in CDownloadManager::DLM_AddTransferRequest(host, port...) and CDownloadManager::DM_ListenCallBack().


I added support for "simple" lines, in files of banned IP. That is: description: ip. That's in addition of the (already supported) blue tack format, which is: description: from_ip-to_ip. However, a file must be made of only one syntax. 
