I'm am behind a linux firewall, and I haved problem for downloading, connecting,...

I have haded in IPTABLES (kernel 2.4) a rule like:
/sbin/iptables -N FILTER
/sbin/iptables -A FILTER -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -A FILTER -p tcp --dport 6346 -j ACCEPT

try ...