DC++ for Linux

yum install linuxdcpp

In active mode, the linux firewall blocks the incoming connections for dc++ , it only works in passive mode
(details about active and passive modes is given here. In a nutshell, in active mode the user directly establishes a connection with the peer and downloads data, whereas in passive mode all data transfer is routed through the hub. So the passive mode is slower)

In effect, you can connect open filelists, search, others can download from you but you can't download from others.

Reason - outgoing connections are allowed, incoming connections are blocked. You initiate a connection to the hub, so its allowed. Opening a filelist and searching, are done through the hub, so that happens. When someone tries to download from you, the hub directs your machine to establish a connection with that peer and send the requested file, so that's allowed too. But when you try to download from peer X, the hub asks peer X to establish a connection with you, peer X (poor honest fellow) tries, but incoming connections on your machine are blocked except on some trusted ports.

Solution - DC++ in active mode will choose any random port for incoming connections. In order to specify a particular port so that you can allow your firewall to let that connection through, select the "firewall with manual port forward" connection mode and enter any port number between 1024 and 65535. Update your firewall settings.. you're done!