Pidgin tranfer files over Bonjour protocol

Hi all,
i’ve discovered this serverless method to chat with other people in the same lan.

I know that in firewall the 5298 tpc port must be opened anc the basic communication works!

The strange thing is that i’m able to send files only by stopping firewall on both the pcs, so with netstat i’ve discovered that the port that pidgin uses to send files changes on every transfer. How to change that? I can’t leave my firewall down!