A router has an inbuilt firewall that block ports by default.

DC++ needs the "ports" to be open in order to be able to search and download in active mode.

So how do you open the ports?

First thing you should do is to go to : www.canyouseeme.org to check if the ports that you would like to use for dc++ are visible from the outside. Remember that you an choose any ports you like above 1500 under normal circumstances.

When you get the result, continue by answering the question here below.